fix(pan-cordio): Wrap call to wsfOsReadyToSleep in a critical section

The function wsfOsReadyToSleep should only be called when interrupts are
disabled. Entering a critical section before calling the function fixes
any potential issues.

features/FEATURE_BLE/targets/TARGET_CORDIO/source/CordioBLE.cpp

@@ -17,6 +17,7 @@
 #include "mbed.h"
 #include "us_ticker_api.h"
 #include "BLE.h"
+#include "CriticalSectionLock.h"
 #include "wsf_types.h"
 #include "wsf_msg.h"
 #include "wsf_os.h"
@@ -412,6 +413,8 @@ void BLE::callDispatcher()
 
     wsfOsDispatcher();
 
+    CriticalSectionLock critical_section;
+
     if (wsfOsReadyToSleep()) {
         static Timeout nextTimeout;
         // setup an mbed timer for the next Cordio timeout