[SCSI] 3w-xxxx: fix oops caused by incorrect REQUEST_SENSE handling

3w-xxxx emulates a REQUEST_SENSE response by simply returning nothing.
Unfortunately, it's assuming that the REQUEST_SENSE command is
implemented with use_sg == 0, which is no longer the case.  The oops
occurs because it's clearing the scatterlist in request_buffer instead
of the memory region.

This is fixed by using tw_transfer_internal() to transfer correctly to
the scatterlist.

Acked-by: adam radford <aradford@gmail.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>