can: flexcan: Unlock the MB unconditionally

Unlock the MB irrespective of reception method being FIFO or timestamp
based. It is optional but recommended to unlock Mailbox as soon as
possible and make it available for reception.

Reported-by: Alexander Stein <alexander.stein@systec-electronic.com>
Signed-off-by: Pankaj Bansal <pankaj.bansal@nxp.com>
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/flexcan.c

@@ -720,9 +720,14 @@ static unsigned int flexcan_mailbox_read(struct can_rx_offload *offload,
 			priv->write(BIT(n - 32), &regs->iflag2);
 	} else {
 		priv->write(FLEXCAN_IFLAG_RX_FIFO_AVAILABLE, &regs->iflag1);
-		priv->read(&regs->timer);
 	}
 
+	/* Read the Free Running Timer. It is optional but recommended
+	 * to unlock Mailbox as soon as possible and make it available
+	 * for reception.
+	 */
+	priv->read(&regs->timer);
+
 	return 1;
 }