linux-phytec-fsl

cw1200: Fix OOPS in monitor mode

In monitor mode, priv->vif is NULL, but at one point in the receive path we
blindly attempt to dereference it.  Add a test to prevent this.

Signed-off-by: Solomon Peachy <pizza@shaftnet.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>