commit 5178b7cd upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>