xen/arm: initialize access

xen/arm: initialize access

Initialize variable *access before returning it back to the caller.
It makes the code a bit nicer and it is a safety certification
requirement.

M3CM Rule-9.1: The value of an object with automatic storage duration
shall not be read before it has been set

QAVerify: 2962
Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>
Acked-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Acked-by: Julien Grall <julien.grall@arm.com>
CC: rcojocaru@bitdefender.com
CC: Tamas K Lengyel <tamas@tklengyel.com>