NFC: trf7970a: Clear possible spurious interrupt before transmitting

The trf7970a occasionally generates spurious interrupts
which can confuse the driver.  To help alleviate this,
clear any interrupts by reading the 'IRQ Status Register'
before starting a new transaction.

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

drivers/nfc/trf7970a.c

@@ -1120,6 +1120,7 @@ static int trf7970a_in_send_cmd(struct nfc_digital_dev *ddev,
 	char *prefix;
 	unsigned int len;
 	int ret;
+	u8 status;
 
 	dev_dbg(trf->dev, "New request - state: %d, timeout: %d ms, len: %d\n",
 			trf->state, timeout, skb->len);
@@ -1195,6 +1196,11 @@ static int trf7970a_in_send_cmd(struct nfc_digital_dev *ddev,
 
 	len = min_t(int, skb->len, TRF7970A_FIFO_SIZE);
 
+	/* Clear possible spurious interrupt */
+	ret = trf7970a_read_irqstatus(trf, &status);
+	if (ret)
+		goto out_err;
+
 	ret = trf7970a_transmit(trf, skb, len);
 	if (ret) {
 		kfree_skb(trf->rx_skb);