sata_rcar: kill superfluous code in sata_rcar_bmdma_fill_sg()

I've modified sata_rcar_bmdma_fill_sg() to take care of splitting long
scatter/ gather segments due to the descriptor table transfer counter
being only 28 bits wide (bit 1 to bit 28) but that was in vain as even
if 'sata_rcar_sht' specified a correct 'dma_boundary' field, the DMA
and block layers would have split the S/G segments on the necassary
boundaries. Since the driver uses ATA_BMDMA_SHT() to initilaize
'sata_rcar_sht', the boundary is much smaller, only 0xFFFF, so the
code I've added is even more useless, and it's better to just remove
it.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Tejun Heo <tj@kernel.org>