[fix] aarch32: optee: define the OP-TEE secure payload

As per MISRA C-2012 Rule 10.4.
arg0 is a u_register_t, can be a 32bit or 64bit upon architecture.

Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
diff --git a/bl2/bl2_image_load_v2.c b/bl2/bl2_image_load_v2.c
index 198b65e..f94378a 100644
--- a/bl2/bl2_image_load_v2.c
+++ b/bl2/bl2_image_load_v2.c
@@ -88,7 +88,7 @@
 	assert(bl2_to_next_bl_params->head->ep_info);
 
 	/* Populate arg0 for the next BL image if not already provided */
-	if (bl2_to_next_bl_params->head->ep_info->args.arg0 == 0)
+	if (bl2_to_next_bl_params->head->ep_info->args.arg0 == (u_register_t)0)
 		bl2_to_next_bl_params->head->ep_info->args.arg0 =
 					(u_register_t)bl2_to_next_bl_params;