[SCSI] ips: fix data buffer accessors conversion bug

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>
Cc: Stable Tree <stable@kernel.org>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>