can: flexcan: poll MCR_LPM_ACK instead of GPR ACK for stop mode acknowledgment

commit 048e3a34 upstream.

Stop Mode is entered when Stop Mode is requested at chip level and
MCR[LPM_ACK] is asserted by the FlexCAN.

Double check with IP owner, the MCR[LPM_ACK] bit should be polled for
stop mode acknowledgment, not the acknowledgment from chip level which
is used to gate flexcan clocks.

This patch depends on:

    b7603d08 ("can: flexcan: add low power enter/exit acknowledgment helper")

Fixes: 5f186c25

 (can: flexcan: fix stop mode acknowledgment)
Tested-by: Sean Nyekjaer <sean@geanix.com>
Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Cc: linux-stable <stable@vger.kernel.org> # >= v5.0
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>