USB: Prepare for refactoring by adding extra udev checks.

[This is upstream commit 2d4fa940.
It needs to be backported to kernels as old as 3.2, because it fixes the
buggy commit 65bdac5e "USB: Handle warm
reset failure on empty port."]

The next patch will refactor the hub port code to rip out the recursive
call to hub_port_reset on a failed hot reset.  In preparation for that,
make sure all code paths can deal with being called with a NULL udev.
The usb_device will not be valid if warm reset was issued because a port
transitioned to the Inactive or Compliance Mode on a device connect.

This patch should have no effect on current behavior.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>