bitops: protect find_first_{,zero}_bit properly

bitops: protect find_first_{,zero}_bit properly

find_first_bit() and find_first_zero_bit() are not protected with
ifdefs as other functions in find.h. It causes build errors on some
platforms if CONFIG_GENERIC_FIND_FIRST_BIT is enabled.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
Fixes: 538057c80942 ("lib: add fast path for find_first_*_bit() and find_last_bit()")
Reported-by: kernel test robot <lkp@intel.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>