[SCSI] lpfc: add missed data buffer accessor

This is an addendum to:

 commit a0b4f78f
 Author: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
    [SCSI] lpfc: convert to use the data buffer accessors

One place was missed in the merge

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Acked-by: James Smart <James.Smart@Emulex.Com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>