SPM: Optimize the PSA API error handling process

In SPM implementation, message is a struct inside connection
handle struct and therefore it is unnecessary to check whether
the message pointer is NULL.

This patch:
- Skips checking message pointer after getting it from the
  connection handle.
- Returns an error code instead of calling tfm_core_panic()
  in some error processing.

Change-Id: Id45e63f8bbdd3d21db3ee32b43f4553ab7520a8f
Signed-off-by: Mingyang Sun <mingyang.sun@arm.com>
3 files changed