ath9k: update the MCS mask for MCS16 and above

Signed-off-by: NFelix Fietkau <nbd@openwrt.org>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/xmit.c

@@ -19,7 +19,7 @@
 
 #define BITS_PER_BYTE           8
 #define OFDM_PLCP_BITS          22
-#define HT_RC_2_MCS(_rc)        ((_rc) & 0x0f)
+#define HT_RC_2_MCS(_rc)        ((_rc) & 0x1f)
 #define HT_RC_2_STREAMS(_rc)    ((((_rc) & 0x78) >> 3) + 1)
 #define L_STF                   8
 #define L_LTF                   8