bus: fsl-mc: Check return value of platform_get_resource()

platform_get_resource() returns NULL in case of failure, so check its
return value and propagate the error in order to prevent NULL pointer
dereference.

Fixes: 6305166c ("bus: fsl-mc: Add ACPI support for fsl-mc")
Cc: stable@vger.kernel.org
Signed-off-by: Salah Triki <salah.triki@gmail.com>
Acked-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Link: https://lore.kernel.org/r/aKwuK6TRr5XNYQ8u@pc


Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>