hpsa: Fix -Wunused-but-set-variable warning

Remove unused variable in hpsa_free_cmd_pool.

Reviewed-by: Scott Teel <scott.teel@pmcs.com>
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Acked-by: Don Brace <don.brace@pmcs.com>
Signed-off-by: Don Brace <don.brace@pmcs.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>