ASoC: ab8500: Fix invalid cast to long pointer

Don't cast to long pointers blindly just for using find_first_bit()
and co.  This is certainly not portable at all.

Reimplement the code with ffs() and fls() instead.  This is a slight
optimization, too.

Spotted by coverity CID 1056484 and 1056485.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mark Brown <broonie@linaro.org>