cciss: Inform controller we are using 32-bit tags.

Controller will DMA only 32-bits of the tag per command
on completion if it knows we are only using 32-bit tags.

Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>