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

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

Fixes: aef85b56 ("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>