[SCSI] Fix incorrect pointer in megaraid.c MODE_SENSE emulation

The SCSI megaraid drive goes to great effort to kmap
the scatterlist buffer (if used), but then uses the
wrong pointer when copying to it afterward.

Signed-off-by: Mark Lord <lkml@rtr.ca>
Acked by: Ju, Seokmann <Seokmann.Ju@engenio.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>