Only the address needs alignment of mask bits, length should work with
a relaxed alignment check.
Signed-off-by: NJens Axboe <axboe@suse.de>

[ This is take 2: make the length check be for 16-byte alignment, not
  just word alignment.  That should hopefully keep everybody happy,
  while still allowing CD writing with DMA ]
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>