usb: gadget: fix unused-but-set-variale warnings

Those are enabled with W=1 make option.

The patch leaves of some type-limits warnings which are caused by
generic macros used in a way where they produce always-false
conditions.

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
index 3580f19..6ded634 100644
--- a/drivers/usb/gadget/function/u_serial.c
+++ b/drivers/usb/gadget/function/u_serial.c
@@ -907,7 +907,6 @@
 {
 	struct gs_port	*port = tty->driver_data;
 	unsigned long	flags;
-	int		status;
 
 	pr_vdebug("gs_write: ttyGS%d (%p) writing %d bytes\n",
 			port->port_num, tty, count);
@@ -917,7 +916,7 @@
 		count = gs_buf_put(&port->port_write_buf, buf, count);
 	/* treat count == 0 as flush_chars() */
 	if (port->port_usb)
-		status = gs_start_tx(port);
+		gs_start_tx(port);
 	spin_unlock_irqrestore(&port->port_lock, flags);
 
 	return count;