Reorder request_queue to remove 16 bytes of alignment padding in 64 bit
builds.

On my config this shrinks the size of this structure from 1608 to 1592
bytes and therefore needs one fewer cachelines.

Also trivially move the open bracket { to be on the same line as the
structure name to make it easier to grep.
Signed-off-by: NRichard Kennedy <richard@rsk.demon.co.uk>
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>