staging: usbip: bugfix for deadlock

Interrupts must be disabled prior to calling usb_hcd_unlink_urb_from_ep.
If interrupts are not disabled, it can potentially lead to a deadlock.
The deadlock is readily reproduceable on a slower (ARM based) device
such as the TI Pandaboard.

Signed-off-by: Bart Westgeest <bart@elbrys.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>