plat: fix switch statements to comply with MISRA rules

Ensure (where possible) that switch statements in plat comply with MISRA
rules 16.1 - 16.7.

Change-Id: Ie4a7d2fd10f6141c0cfb89317ea28a755391622f
Signed-off-by: Jonathan Wright <jonathan.wright@arm.com>
diff --git a/plat/mediatek/common/custom/oem_svc.c b/plat/mediatek/common/custom/oem_svc.c
index 08baed8..49e7571 100644
--- a/plat/mediatek/common/custom/oem_svc.c
+++ b/plat/mediatek/common/custom/oem_svc.c
@@ -41,15 +41,8 @@
 			void *handle,
 			uint64_t flags)
 {
-	uint64_t rc;
-
-	switch (smc_fid) {
-	default:
-		rc = SMC_UNK;
-		WARN("Unimplemented OEM Call: 0x%x\n", smc_fid);
-	}
-
-	SMC_RET1(handle, rc);
+	WARN("Unimplemented OEM Call: 0x%x\n", smc_fid);
+	SMC_RET1(handle, SMC_UNK);
 }
 
 /*