m68k: bitops: Change __fls to return and accept unsigned long

m68k: bitops: Change __fls to return and accept unsigned long

As per asm-generic definition and other architectures __fls should
return and accept unsigned long as its parameter.

No functional change is expected as return value should fit in unsigned
long.

Reviewed-by: Cezary Rojewski <cezary.rojewski@intel.com>
Signed-off-by: Amadeusz Sławiński <amadeuszx.slawinski@linux.intel.com>
Link: https://lore.kernel.org/r/20220527115345.2588775-3-amadeuszx.slawinski@linux.intel.com
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>