Const correctness

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 1549562..8af26d3 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -3713,7 +3713,7 @@
     return( status );
 }
 
-static psa_status_t psa_aead_final_checks( psa_aead_operation_t *operation )
+static psa_status_t psa_aead_final_checks( const psa_aead_operation_t *operation )
 {
     if( operation->id == 0 || !operation->nonce_set )
         return( PSA_ERROR_BAD_STATE );