[PATCH] bcm43xx: Fix bug in frequency to channel conversion

The frequency to channel routine in bcm43xx requires that the frequency
be in MHz, but that condition is not always met. This patch does the
necessary conversion.

Signed-off-by: Joerg Sommer <joerg@alea.gnuu.de>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>