usb: core: remove flags variable in __usb_hcd_giveback_urb()

In commit ed194d1367698 ("usb: core: remove local_irq_save() around
->complete() handler") I removed the only user of the flags variable and
forgot to remove the variable, leading to warning because it is unused
now.
Remove the unused variable.

Fixes: ed194d1367698 ("usb: core: remove local_irq_save() around ->complete() handler")
Reported-by: Stephen Rothwell <[e-mail]>
Signed-off-by: Sebastian Andrzej Siewior <[e-mail]>
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/core/hcd.c

···
 	struct usb_hcd *hcd = bus_to_hcd(urb->dev->bus);
 	struct usb_anchor *anchor = urb->anchor;
 	int status = urb->unlinked;
-	unsigned long flags;
 
 	urb->hcpriv = NULL;
 	if (unlikely((urb->transfer_flags & URB_SHORT_NOT_OK) &&