USB: fix previous sparse fix which was incorrect

The previous fix for a "sparse" warning in ehci_urb_dequeue() was
incorrect.  After rescheduling interrupt transfers it returned the
URB's completion status, not status for the dequeue operation itself.

This patch resolves that issue, cleans up the code in the reschedule
path, and shrinks the object code by a dozen bytes.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>