aic7xxx_old: removed unused 'req' variable

After the patch "block: remove spurious uses of REQ_HARDBARRIER",
we no longer use 'req' in aic7xxx_buildscb(). Kill it.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>