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/common/plat_gicv3.c b/plat/common/plat_gicv3.c
index cf9aca2..26a4973 100644
--- a/plat/common/plat_gicv3.c
+++ b/plat/common/plat_gicv3.c
@@ -247,6 +247,7 @@
 		break;
 	default:
 		assert(0);
+		break;
 	}
 
 	gicv3_set_spi_routing(id, irm, mpidr);