gcc -pedantic cleaning patch (function pointer to/from object pointer casting)

[maqifrnswa]

Building with target_compile_options(proj_name PRIVATE -Wpedantic), there are a bunch of extra warnings in the sdk. I fixed the ones I saw for the rp2040 here:
maqifrnswa@7253859

I wanted to check to see if there's an interest in cleaning these up. If so, I can work through the rp2350 as well and prepare a better commit.

Summary:

1. Most of them are for casting function pointers to/from object pointers (/.pico-sdk/sdk/2.1.0/src/rp2_common/hardware_flash/flash.c:120:65: warning: ISO C forbids conversion of object pointer to function pointer type [-Wpedantic]).
   I went through and changed functions that returned function pointers from:
   void *function_name(args); // which is a function that returns a pointer to data
   to
   void (* function_name(args))(void); // a func. that returns a function pointer
   Some functions return a data pointer or a func pointer, so I changed them from:
   void *function_name(args);
   to
   uintptr_t function_name(args); // this allows casting to either a func or data pointer
   To be super-super-super pedantic, things should be specific about whether they are returning a function pointer or data pointer. uintptr_t isn't ideal for function pointers, but I think (IMO) it's fine to use uintptr_t with these architectures since it is often used for cases like this where you have a ROM address that may be a function or data.

2. a couple stray ; from ISO C does not allow extra ';' outside of a function [-Wpedantic]

3. converted binary constants to hex binary constants are a C2X feature or GCC extension