Removed the static modifier from the usb module.

f3/usb/src/usb.c

@@ -22,7 +22,7 @@ unsigned short int usb_dma_phase_write_ptr;
   * @param  None
   * @retval Result of the operation: USBD_OK if all operations are OK else USBD_FAIL
   */
-static int8_t usb_cdc_init(void)
+int8_t usb_cdc_init(void)
 {
   /* USER CODE BEGIN 3 */
   /* Set Application Buffers */
@@ -45,7 +45,7 @@ static int8_t usb_cdc_init(void)
   * @param  None
   * @retval Result of the operation: USBD_OK if all operations are OK else USBD_FAIL
   */
-static int8_t usb_cdc_deinit(void)
+int8_t usb_cdc_deinit(void)
 {
   /* USER CODE BEGIN 4 */
   return (USBD_OK);
@@ -60,7 +60,7 @@ static int8_t usb_cdc_deinit(void)
   * @param  length: Number of data to be sent (in bytes)
   * @retval Result of the operation: USBD_OK if all operations are OK else USBD_FAIL
   */
-static int8_t usb_cdc_control(uint8_t cmd, uint8_t* pbuf, uint16_t length)
+int8_t usb_cdc_control(uint8_t cmd, uint8_t* pbuf, uint16_t length)
 {
   /* USER CODE BEGIN 5 */
   switch (cmd)
@@ -138,7 +138,7 @@ static int8_t usb_cdc_control(uint8_t cmd, uint8_t* pbuf, uint16_t length)
   * @param  Len: Number of data received (in bytes)
   * @retval Result of the operation: USBD_OK if all operations are OK else USBD_FAIL
   */
-static int8_t usb_cdc_receive(uint8_t* Buf, uint32_t *Len)
+int8_t usb_cdc_receive(uint8_t* Buf, uint32_t *Len)
 {
   int i=0;