uas: improve device reset

Add new function to unlink and abort requests from the work
list, call it on bus reset and disconnect where we kill all
in-flight urbs.  Also reorder calls in disconnect to first
cancel transfers, then remove the scsi hba.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>