ath5k: fix regression on setting bssid mask on association

There was a typo on the second bssid mask register.
This was caused by the patch titled:

"ath5k: use common curbssid, bssidmask and macaddr"

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath5k/pcu.c b/drivers/net/wireless/ath/ath5k/pcu.c
index 9ac7638..0385e80 100644
--- a/drivers/net/wireless/ath/ath5k/pcu.c
+++ b/drivers/net/wireless/ath/ath5k/pcu.c
@@ -292,7 +292,7 @@
 		ath5k_hw_reg_write(ah, get_unaligned_le32(common->bssidmask),
 				   AR_BSSMSKL);
 		ath5k_hw_reg_write(ah,
-				   get_unaligned_le16(common->curbssid + 4),
+				   get_unaligned_le16(common->bssidmask + 4),
 				   AR_BSSMSKU);
 	}