fix(spm): reference to ffa_value struct fields

Some verbose message logs in TF-A-Tests needed to be
updated in accordance to [1].
In the referred patch a common structure was introduced
for ff-a calls. This patch fixes pending changes in
verbose log messages.

[1] https://review.trustedfirmware.org/c/TF-A/tf-a-tests/+/14733



Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: Ib20919d1933f601ed36d9f1011c94193adf4847a