bitops: Update kernel-doc in hweight.c to fix the issues with it

bitops: Update kernel-doc in hweight.c to fix the issues with it

The kernel-doc in lib/hweight.c is global to  the file and
currently has issues:

Warning: lib/hweight.c:13 expecting prototype for hweightN(). Prototype was for __sw_hweight32() instead
Warning: lib/hweight.c:13 function parameter 'w' not described in '__sw_hweight32'

Update it accordingly.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>