dm error: mark as DM_TARGET_PASSES_INTEGRITY

Mark dm error as DM_TARGET_PASSES_INTEGRITY so that it can be stacked on
top of PI capable devices.  The claim is strictly speaking as lie as dm
error fails all I/O and doesn't pass anything on, but doing the same for
integrity I/O work just fine :)

This helps to make about two dozen xfstests test cases pass on PI capable
devices.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>