b43: Use cordic algorithm from kernel library

Kernel library has a common cordic algorithm which is identical
to internally implemented one, so use it and drop the duplicate
implementation.

Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Priit Laes <plaes@plaes.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>