sata_rcar: correct 'sata_rcar_sht'

Using ATA_BMDMA_SHT() to intialize 'sata_rcar_sht' was suboptimal as
the R-Car descriptor table transfer counter is 28 bits wide (bit 1 to
bit 28), so that the 'dma_boundary' field of 0xFFFF is just too small,
as well as the 'sg_tablesize' field of 128.  Use ATA_BASE_SHT() to
initialize 'sata_rcar_sht' instead and give proper values to the
'dma_boundary' and 'sg_tablesize' fields explicitly.

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