services/spm: Fix service UUID lookup

services/spm: Fix service UUID lookup

The spm_sp_get_by_uuid() function is used to look up the secure
partition that provides a given service.

Within this function, memcmp() is used to compare the service
UUIDs but it uses the size of the rdsvc->uuid pointer instead of
the size of its content (missing dereference). This means that only
a partial comparison is performed as UUIDs are 128 bits in length and
rdsvc->uuid is a uint32_t typed pointer.

Instead, use the size of the array pointed to by the svc_uuid parameter,
which will be the full 128 bits, for the comparison.

Change-Id: I258fb0cca3bf19f97b8f2a4c133981647cd050e4
Signed-off-by: Paul Beesley <paul.beesley@arm.com>