Revert "block: Remove extra discard_alignment from hd_struct."

It was not a good idea to start dereferencing disk->queue from
the fs sysfs strategy for displaying discard alignment. We ran
into first a NULL pointer deref, and after fixing that we sometimes
see unvalid disk->queue pointer values.

Since discard is the only one of the bunch actually looking into
the queue, just revert the change.

This reverts commit 23ceb5b7719e9276d4fa72a3ecf94dd396755276.

Conflicts:
	fs/partitions/check.c