ata: sata_rcar: Use of_device_get_match_data() helper

Use the of_device_get_match_data() helper instead of open coding.
Note that the sata_rcar driver is used with DT only, so there's always a
valid match.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Tejun Heo <tj@kernel.org>