bus: fsl-mc: add back accidentally dropped error check

bus: fsl-mc: add back accidentally dropped error check

[ Upstream commit 61243c03dde238170001093a29716c2369e8358f ]

A previous patch accidentally dropped an error check, so add it back.

Fixes: aef85b56c3c1 ("bus: fsl-mc: MC control registers are not always available")
Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Link: https://lore.kernel.org/r/20201105153050.19662-1-laurentiu.tudor@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>