UPSTREAM: firmware: arm_ffa: Check xa_load() return value

Add a check to verify the result of xa_load() during the partition
lookups done while registering/unregistering the scheduler receiver
interrupt callbacks and while executing the main scheduler receiver
interrupt callback handler.

Bug: 254441685
Fixes: 0184450b ("firmware: arm_ffa: Add schedule receiver callback mechanism")
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/20240108-ffa_fixes_6-8-v1-3-75bf7035bc50@arm.com


Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
(cherry picked from commit c00d9738)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: I49366d27294bf9133f2b57076f888a6347e14742