fix(psa): add missing semicolon

Fix a syntax error in the delegated attestation service code.

Unfortunately, this build failure was not caught by the CI system
because right now lib/psa/delegated_attestation.c file is not getting
pulled in by any upstream platform. This will be addressed in a
separate patch.

Change-Id: Idb84f62aabc5008396213023fc40547097925860
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>