Fix typos prior to release

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>

library/timing.c

@@ -262,7 +262,7 @@ static void TimerProc( void *TimerContext )
     Sleep( alarmMs );
     mbedtls_timing_alarmed = 1;
     /* _endthread will be called implicitly on return
-     * That ensures execution of thread funcition's epilogue */
+     * That ensures execution of thread function's epilogue */
 }
 
 void mbedtls_set_alarm( int seconds )