Fix: testing for mpu wrapers to be equal to 1 (#285)

Author: alfred2g

include/mpu_wrappers.h

@@ -29,7 +29,7 @@
 
 /* This file redefines API functions to be called through a wrapper macro, but
  * only for ports that are using the MPU. */
-#ifdef portUSING_MPU_WRAPPERS
+#if ( portUSING_MPU_WRAPPERS == 1 )
 
 /* MPU_WRAPPERS_INCLUDED_FROM_API_FILE will be defined when this file is
  * included from queue.c or task.c to prevent it from having an effect within