Fix missed invalid specifier in PSA Crypto build

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/programs/ssl/ssl_client2.c b/programs/ssl/ssl_client2.c
index d0758bc..3937981 100644
--- a/programs/ssl/ssl_client2.c
+++ b/programs/ssl/ssl_client2.c
@@ -1667,7 +1667,7 @@
                                                PSA_ALG_SHA_256 ) ) != 0 )
         {
             mbedtls_printf( " failed\n  !  "
-                            "mbedtls_pk_wrap_as_opaque returned -0x%x\n\n", -ret );
+                            "mbedtls_pk_wrap_as_opaque returned -0x%x\n\n", (unsigned int)  -ret );
             goto exit;
         }
     }