jtag/drivers/vsllink: fix memory leak

Close libusb context in vsllink_quit()

Change-Id: I85da8d7228b1b2b033a32b2f9ae9ed0726546b55
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: https://review.openocd.org/c/openocd/+/6766
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

src/jtag/drivers/vsllink.c

@@ -273,6 +273,7 @@ static int vsllink_quit(void)
 	vsllink_free_buffer();
 	vsllink_usb_close(vsllink_handle);
 
+	libusb_exit(vsllink_handle->libusb_ctx);
 	free(vsllink_handle);
 
 	return ERROR_OK;