SCSI ips: fix data buffer accessors conversion bug

commit: 2b28a472

This fixes a bug that can't handle a passthru command with more than
two sg entries.

Big thanks to Tim Pepper for debugging the problem.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: Mark Salyzyn <Mark_Salyzyn@adaptec.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>