hpsa: performance tweak for hpsa_scatter_gather()

Divide the loop in hpsa_scatter_gather() into two, one for the initial SG list
and a second one for the chained list, if any.  This allows the conditional
check which resets the indicies for the chained list to be performed outside
the loop instead of being done on every iteration inside the loop.

Reviewed-by: Scott Teel <scott.teel@pmcs.com>
Reviewed-by: Kevin Barnett <kevin.barnett@pmcs.com>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Reviewed-by: Hannes Reinecke <hare@Suse.de>
Signed-off-by: Webb Scales <webbnh@hp.com>
Signed-off-by: Don Brace <don.brace@pmcs.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: James Bottomley <JBottomley@Odin.com>