Two small fixes

[jdoumont]

Dear mberckx,

Peter Blaha shared your repository with me, as we had discussed the possibility of a docker container for Wien2k at some point. I tried to run your container and ran into two small issues:

1. Something seemed to be wrong with the variable substitution in the makefile. I'm not a GNU make expert, but with the following changes it works for me.
2. I suspect you use a Mac with Apple silicon, as the architecture of openblas was hardcoded to 'aarch64' in the siteconfig inputs. I changed it to $uname -m which should expand to the architecture of the system (x86_64 in my case). With this change, the setup should be portable.

I opened this PR as I thought you might be interested in these changes.

Best regards,
Jan Doumont