Enable fallback to software implementation in psa_sign/verify_message driver

Signed-off-by: gabor-mezei-arm <gabor.mezei@arm.com>
diff --git a/library/psa_crypto_driver_wrappers.c b/library/psa_crypto_driver_wrappers.c
index 95daf80..aab66ab 100644
--- a/library/psa_crypto_driver_wrappers.c
+++ b/library/psa_crypto_driver_wrappers.c
@@ -126,7 +126,7 @@
         default:
             /* Key is declared with a lifetime not known to us */
             (void)status;
-            return( PSA_ERROR_INVALID_ARGUMENT );
+            break;
     }
 
     return( psa_sign_message_builtin( attributes,
@@ -198,7 +198,7 @@
         default:
             /* Key is declared with a lifetime not known to us */
             (void)status;
-            return( PSA_ERROR_INVALID_ARGUMENT );
+            break;
     }
 
     return( psa_verify_message_builtin( attributes,