lib: fix switch statements to comply with MISRA rules

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

Change-Id: I52bc896fb7094d2b7569285686ee89f39f1ddd84
Signed-off-by: Jonathan Wright <jonathan.wright@arm.com>
diff --git a/lib/psci/psci_main.c b/lib/psci/psci_main.c
index d25d177..607d0cd 100644
--- a/lib/psci/psci_main.c
+++ b/lib/psci/psci_main.c
@@ -414,10 +414,12 @@
 		case PSCI_SYSTEM_OFF:
 			psci_system_off();
 			/* We should never return from psci_system_off() */
+			break;
 
 		case PSCI_SYSTEM_RESET:
 			psci_system_reset();
 			/* We should never return from psci_system_reset() */
+			break;
 
 		case PSCI_FEATURES:
 			return psci_features(x1);