Core: Avoid using raw type 'int'

Change tfm_core_set_secure_exception_priorities() return type from
'int' to 'int32_t'.

Change-Id: I4ad925efecd6cf6c3c3e05c72a2282a502aad485
Signed-off-by: Edison Ai <edison.ai@arm.com>
diff --git a/secure_fw/core/tfm_core.c b/secure_fw/core/tfm_core.c
index c18f846..d56e5c9 100644
--- a/secure_fw/core/tfm_core.c
+++ b/secure_fw/core/tfm_core.c
@@ -170,7 +170,7 @@
     return TFM_SUCCESS;
 }
 
-static int tfm_core_set_secure_exception_priorities(void)
+static int32_t tfm_core_set_secure_exception_priorities(void)
 {
     enum tfm_plat_err_t plat_err = TFM_PLAT_ERR_SYSTEM_ERR;