[SCSI] sym2: Remove code to handle DMA_BIDIRECTION requests

The upper layer doesn't send these down since 2.4.x (or 2.6 in
practice), so no need to handle it.  Inline sym_setup_data_pointers
into its only caller so we can fail gracefully in the case we'd get
one neverless.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>