usbatm: Detect usb device shutdown and ignore failed urbs

Detect usb device shutdown and ignore failed urbs.  This happens when the
driver is unloaded or the device is unplugged.

I'm not sure what other urb statuses should be ignored, and the warning
message doesn't need to be shown when the module is unloaded or the device
is removed.

Signed-off-by: Simon Arlott <simon@fire.lp0.eu>
Cc: Duncan Sands <duncan.sands@math.u-psud.fr>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>