USBMSD: force internal flash for nRF52 only

Author: facchinm

libraries/USBMSD/Singleton.cpp

@@ -78,6 +78,7 @@ class FlashIAPBlockDeviceMutexFriendly: public FlashIAPBlockDevice {
 */
 
 //static FlashIAPBlockDeviceMutexFriendly bd(0x80000, 0x80000);
+#ifdef NRF52840_XXAA
 static FlashIAPBlockDevice bd(0x80000, 0x80000);
 
 void USBMSD::begin()
@@ -94,4 +95,6 @@ mbed::FATFileSystem& USBMSD::getFileSystem()
 	return fs;
 }
 
-USBMSD MassStorage(&bd);
+USBMSD MassStorage(&bd);
+
+#endif