USB: serial: quatech2: remove unused qt2_setdevice function

clang with W=1 reports
drivers/usb/serial/quatech2.c:179:19: error: unused function
  'qt2_setdevice' [-Werror,-Wunused-function]
static inline int qt2_setdevice(struct usb_device *dev, u8 *data)
                  ^
This function is not used, so remove it.
Signed-off-by: Tom Rix <trix@redhat.com>
Link: https://lore.kernel.org/r/20230321181255.1825963-1-trix@redhat.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/quatech2.c

@@ -176,14 +176,6 @@ static inline int qt2_control_msg(struct usb_device *dev,
 			       NULL, 0, QT2_USB_TIMEOUT);
 }
 
-static inline int qt2_setdevice(struct usb_device *dev, u8 *data)
-{
-	u16 x = ((u16) (data[1] << 8) | (u16) (data[0]));
-
-	return qt2_control_msg(dev, QT_SET_GET_DEVICE, x, 0);
-}
-
-
 static inline int qt2_getregister(struct usb_device *dev,
 				  u8 uart,
 				  u8 reg,