NFC: trf7970a: Don't turn off RF if its already off

Don't try to turn off of RF transmitter is its
already off.

Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/nfc/trf7970a.c

@@ -859,6 +859,10 @@ err_out:
 
 static void trf7970a_switch_rf_off(struct trf7970a *trf)
 {
+	if ((trf->state == TRF7970A_ST_PWR_OFF) ||
+			(trf->state == TRF7970A_ST_RF_OFF))
+		return;
+
 	dev_dbg(trf->dev, "Switching rf off\n");
 
 	trf->chip_status_ctrl &= ~TRF7970A_CHIP_STATUS_RF_ON;