Move DEVICE_FLASH define to avoid compilation issues for non FLASH devices

targets/TARGET_STM/TARGET_STM32F4/flash_api.c

@@ -28,13 +28,13 @@
  *******************************************************************************
  */
 
+#if DEVICE_FLASH
 #include "flash_api.h"
 #include "flash_data.h"
 #include "platform/mbed_critical.h"
 
 // This file is automatically generated
 
-#if DEVICE_FLASH
 
 static uint32_t GetSector(uint32_t Address);
 static uint32_t GetSectorSize(uint32_t Sector);