staging: vt6656: vnt_rf_setpower: fix missing rate RATE_12M

When the driver sets this rate a power of zero value is set causing
data flow stoppage until another rate is tried.
Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Cc: <stable@vger.kernel.org> # v3.17+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vt6656/rf.c

@@ -640,6 +640,7 @@ int vnt_rf_setpower(struct vnt_private *priv, u32 rate, u32 channel)
 		break;
 	case RATE_6M:
 	case RATE_9M:
+	case RATE_12M:
 	case RATE_18M:
 	case RATE_24M:
 	case RATE_36M: