linux-wandboard

mac80211: silently accept deletion of non-existant key

Otherwise, 'iwconfig wlan0 key off' with no key set results in:

	Error for wireless request "Set Encode" (8B2A) :
	    SET failed on device wlan0 ; No such file or directory.

Signed-off-by: John W. Linville <linville@tuxdriver.com>