Ensure the flow through switch statements is clear

Ensure case clauses:
*   Terminate with an unconditional break, return or goto statement.
*   Use conditional break, return or goto statements as long as the end
    of the case clause is unreachable; such case clauses must terminate
    with assert(0) /* Unreachable */ or an unconditional  __dead2 function
    call
*   Only fallthough when doing otherwise would result in less
    readable/maintainable code; such case clauses must terminate with a
    /* Fallthrough */ comment to make it clear this is the case and
    indicate that a fallthrough is intended.

This reduces the chance of bugs appearing due to unintended flow through a
switch statement

Change-Id: I70fc2d1f4fd679042397dec12fd1982976646168
Signed-off-by: Daniel Boulby <daniel.boulby@arm.com>
diff --git a/services/spd/tspd/tspd_main.c b/services/spd/tspd/tspd_main.c
index 3ec98d6..d2acda8 100644
--- a/services/spd/tspd/tspd_main.c
+++ b/services/spd/tspd/tspd_main.c
@@ -592,6 +592,7 @@
 
 			SMC_RET3(ns_cpu_context, x1, x2, x3);
 		}
+		assert(0); /* Unreachable */
 
 	/*
 	 * Request from the non-secure world to abort a preempted Yielding SMC