wl1271: Don't generate null func template for ad-hoc

The null func template is not needed for ad-hoc, and it's generation is not
supported for ad-hoc (mac80211 will WARN about it.)

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Teemu Paasikivi <ext-teemu.3.paasikivi@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>