We never checked for errors on add_disk() as this function returned
void. Now that this is fixed, use the shiny new error handling.

There are two calls to dm_setup_md_queue() which can fail then, one on
dm_early_create() and we can easily see that the error path there
calls dm_destroy in the error path. The other use case is on the ioctl
table_load case. If that fails userspace needs to call the
DM_DEV_REMOVE_CMD to cleanup the state - similar to any other
failure.
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>