cactus: fix access to uninitialized array

Array 'receivers' of 'struct ffa_memory_region' was being accessed
without being initialized, in function 'ffa_memory_management_test'.
Changed it to process 'ffa_memory_region' transaction descriptor
from the partition's mailbox.

Change-Id: If240a3d0bc554558cd06bc8200a2f66d501b7f4f
Signed-off-by: J-Alves <joao.alves@arm.com>
2 files changed