[PATCH] elevator: fixup typo in merge logic

The recent io scheduler allow_merge commit left the block layer with
no merging, oops. This patch fixes that up.

That means the CFQ change needs to be verified again, it might not fix
the original bug now.  But that's a seperate thing, I'll double check
that tomorrow.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>