Fix MPU issue

patches/tock/05-mpu-fix.patch

@@ -0,0 +1,12 @@
+diff --git a/kernel/src/sched.rs b/kernel/src/sched.rs
+index ed3ae8260..f109960d3 100644
+--- a/kernel/src/sched.rs
++++ b/kernel/src/sched.rs
+@@ -632,6 +632,7 @@ impl Kernel {
+                     let context_switch_reason = process.switch_to();
+                     scheduler_timer.disarm();
+                     chip.mpu().disable_app_mpu();
++                    chip.mpu().clear_mpu();
+ 
+                     // Now the process has returned back to the kernel. Check
+                     // why and handle the process as appropriate.