p54: fix p54_set_key's return code

p54 doesn't support AES-128-CMAC offload.

This patch will fix the noisy mac80211 warnings, when 802.11w is enabled:
mac80211-phy189: failed to set key (4, ff:ff:ff:ff:ff:ff) to hardware (-22)
mac80211-phy189: failed to set key (5, ff:ff:ff:ff:ff:ff) to hardware (-22)

Signed-off-by: Christian Lamparter <chunkeey@web.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>