mac80211: Fix misplaced return in AES-GMAC key setup

Commit 8ade538b ("mac80111: Add BIP-GMAC-128 and BIP-GMAC-256
ciphers") had the success return in incorrect place before the
crypto_aead_setauthsize() call which practically ended up skipping that
call unconditionally.

The missing call did not actually change any functionality since
GMAC_MIC_LEN (16) is identical to the maxauthsize in gcm(aes) and as
such, the default value used for the authsize parameter.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>