rtlwifi: Use ffs in <foo>_phy_calculate_bit_shift

[ Upstream commit 6c1d61913570d4255548ac598cfbef6f1e3c3eee ]

Remove the loop and use the generic ffs instead.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/e2ab424d24b74901bc0c39f0c60f75e871adf2ba.camel@perches.com


Stable-dep-of: bc8263083af6 ("wifi: rtlwifi: rtl8821ae: phy: fix an undefined bitwise shift behavior")
Signed-off-by: Sasha Levin <sashal@kernel.org>