set initial DFU state to ERROR if application is corrupt

as specified in DFU standard

Change-Id: Icd503a2d19f829eb43a83c28b526b73d595640f0

usb/class/dfu/device/dfudf.c

@@ -306,7 +306,6 @@ int32_t dfudf_init(void)
 	usbdc_register_function(&_dfudf);
 	usbdc_register_handler(USBDC_HDL_REQ, &dfudf_req_h);
 
-	// TODO check if firmware is corrupted and set dfuERROR state if it is
 	return ERR_NONE;
 }
 

usb_dfu_main.c

@@ -101,6 +101,9 @@ int main(void)
 	if (!check_force_dfu() && check_application()) { // application is valid
 		start_application(); // start application
 	} else {
+		if (!check_application()) { // if the application is corrupted the start DFU start should be dfuERROR
+			dfu_state = USB_DFU_STATE_DFU_ERROR;
+		}
 		usb_dfu(); // start DFU bootloader
 	}
 }