bus: fsl-mc: MC control registers are not always available

As per the device tree binding, in certain scenarios such as
virtualization scenarios, the MC control registers are not
available so don't error out if they are not present.

Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Link: https://lore.kernel.org/r/20200914105459.27448-2-laurentiu.tudor@nxp.com


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