services: fix switch statements to comply with MISRA rules

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

Change-Id: I47bf6ed4a026201e6fe125ce51842482e99e8bb0
Signed-off-by: Jonathan Wright <jonathan.wright@arm.com>
diff --git a/services/spd/tlkd/tlkd_common.c b/services/spd/tlkd/tlkd_common.c
index 483d45b..d846269 100644
--- a/services/spd/tlkd/tlkd_common.c
+++ b/services/spd/tlkd/tlkd_common.c
@@ -49,6 +49,7 @@
 		break;
 	default:
 		assert(0);
+		break;
 	}
 
 	/* get the (NS/S) physical address */