staging: brcm80211: make use of fls bit operation in wlc_phy_compute_dB

wlc_phy_compute_dB converts absolute power value to dB implementing
a fixed point calculation for 10*log10(x). It does this by determining
the most significant bit for value x. This can be done using the fls()
bit operation, which has arch specific and possibly more efficient
implementation.

Cc: devel@linuxdriverproject.org
Cc: linux-wireless@vger.kernel.org
Reviewed-by: Roland Vossen <rvossen@broadcoom.com>
Reviewed-by: Henry Ptasinski <henryp@broadcom.com>
Reviewed-by: Brett Rudley <brudley@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>