USB: serial: io_edgeport: fix possible sleep-in-atomic

According to drivers/usb/serial/io_edgeport.c, the driver may sleep
under a spinlock.
The function call path is:
edge_bulk_in_callback (acquire the spinlock)
   process_rcvd_data
     process_rcvd_status
       change_port_settings
         send_iosp_ext_cmd
           write_cmd_usb
             usb_kill_urb --> may sleep

To fix it, the redundant usb_kill_urb() is removed from the error path
after usb_submit_urb() fails.

This possible bug is found by my static analysis tool (DSAC) and checked
by my code review.
Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/io_edgeport.c

@@ -2282,7 +2282,6 @@ static int write_cmd_usb(struct edgeport_port *edge_port,
 		/* something went wrong */
 		dev_err(dev, "%s - usb_submit_urb(write command) failed, status = %d\n",
 			__func__, status);
-		usb_kill_urb(urb);
 		usb_free_urb(urb);
 		atomic_dec(&CmdUrbs);
 		return status;