b43: LP-PHY: Revert to the original PHY register write routine

After some discussion on IRC about the PHY register write change,
I am not sure anymore if this is the right thing to do.

Signed-off-by: Gábor Stefanik <netrolller.3d@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>