m68k: bitops: Fix find_*_bit() signatures

The function signatures of the m68k-optimized implementations of the
find_{first,next}_{,zero_}bit() helpers do not match the generic
variants.

Fix this by changing all non-pointer inputs and outputs to "unsigned
long", and updating a few local variables.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202509092305.ncd9mzaZ-lkp@intel.com/


Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: "Yury Norov (NVIDIA)" <yury.norov@gmail.com>
Link: https://patch.msgid.link/de6919554fbb4cd1427155c6bafbac8a9df822c8.1757517135.git.geert@linux-m68k.org