staging: vt6656: vnt_rf_setpower rate <= RATE_11M check array bound

decrement channel by one and check array bound.
Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vt6656/rf.c

@@ -744,7 +744,10 @@ int vnt_rf_setpower(struct vnt_private *priv, u32 rate, u32 channel)
 	case RATE_2M:
 	case RATE_5M:
 	case RATE_11M:
-		power = priv->abyCCKPwrTbl[channel-1];
+		channel--;
+
+		if (channel < sizeof(priv->abyCCKPwrTbl))
+			power = priv->abyCCKPwrTbl[channel];
 		break;
 	case RATE_6M:
 	case RATE_9M: