mac80211 : Fix setting ad-hoc mode and non-ibss channel

Patch fixes the kernel trace when user tries to set
ad-hoc mode on non IBSS channel.
e.g iwconfig wlan0 chan 36 mode ad-hoc

Signed-off-by: Abhijeet Kolekar <abhijeet.kolekar@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>