stmhal: Declare variables extern in include files

Else we end up with several instances of the variable.

Signed-off-by: Sven Wegener <sven.wegener@stealer.net>

Author: swegener

stmhal/file.h

@@ -24,6 +24,6 @@
  * THE SOFTWARE.
  */
 
-const byte fresult_to_errno_table[20];
+extern const byte fresult_to_errno_table[20];
 
 MP_DECLARE_CONST_FUN_OBJ(mp_builtin_open_obj);

stmhal/usb.h

@@ -41,7 +41,7 @@ typedef enum {
     USB_STORAGE_MEDIUM_SDCARD,
 } usb_storage_medium_t;
 
-const mp_obj_type_t pyb_usb_vcp_type;
+extern const mp_obj_type_t pyb_usb_vcp_type;
 
 void pyb_usb_init0(void);
 void pyb_usb_dev_init(usb_device_mode_t mode, usb_storage_medium_t medium);