Cleanup make -f build.mk clone warnings.

[mpolitzer]

make -f build.mk clone warnings. Task should be achieved without warnings.

$ make -f build.mk clone                              
make[1]: *** work/linux: No such file or directory.  Stop.                                                  
make[1]: *** work/linux: No such file or directory.  Stop.                                                  
make[1]: *** work/linux: No such file or directory.  Stop.                                                  
make[1]: *** work/linux: No such file or directory.  Stop.                                                  
make[1]: *** work/linux: No such file or directory.  Stop.                                                  
make[1]: *** work/linux: No such file or directory.  Stop.                                                  
make[1]: *** work/linux: No such file or directory.  Stop.                                                  
git clone --depth 1 --branch linux-6.5.9-ctsi-y \                                                           
        [email protected]:cartesi/linux.git work/linux || \                                                    
        cd work/linux && git pull                                                                           
Cloning into 'work/linux'...                          
remote: Enumerating objects: 85938, done.                                                                   
remote: Counting objects: 100% (85938/85938), done.                                                         
remote: Compressing objects: 100% (80882/80882), done.                                                      
remote: Total 85938 (delta 7880), reused 42752 (delta 4153), pack-reused 0                                                                                                                                              
Receiving objects: 100% (85938/85938), 241.78 MiB | 5.70 MiB/s, done.                                                                                                                                                   
Resolving deltas: 100% (7880/7880), done.                                                                   
Updating files: 100% (81118/81118), done.                                                                   
You are not currently on a branch.                                                                          
Please specify which branch you want to merge with.                                                         
See git-pull(1) for details.                          

    git pull <remote> <branch>                                                                              

make: *** [build.mk:110: clone] Error 1