Convert BL31 error message into warning

If BL32 isn't present or it fails to initialize the current code prints
an error message in both debug and release builds. This is too verbose
for release builds, so it has been converted into a warning.

Also, it was missing a newline at the end of the message.

Change-Id: I91e18d5d5864dbb19d47ecd54f174d2d8c06296c
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>

bl31/bl31_main.c

@@ -109,7 +109,8 @@ void bl31_main(void)
 		int32_t rc = (*bl32_init)();
 
 		if (rc != 0) {
-			ERROR("BL31: BL32 initialization failed (rc = %d)", rc);
+			WARN("BL31: BL32 initialization failed (rc = %d)\n",
+			     rc);
 		}
 	}
 	/*