HID: usbhid: fix use-after-free bug

This patch (as1592) fixes an obscure problem in the usbhid driver.
Under some circumstances, a control or interrupt-OUT URB can be
submitted twice.  This will happen if the first submission fails; the
queue pointers aren't updated, so the next time the queue is restarted
the same URB will be submitted again.

The problem is that raw_report gets deallocated during the first
submission.  The second submission will then dereference and try to
free an already-freed region of memory.  The patch fixes the problem
by setting raw_report to NULL when it is deallocated and checking for
NULL before dereferencing it.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>