ata: Drop commas after OF match table sentinels

It does not make sense to have a comma after a sentinel, as any new
elements must be added before the sentinel.

Add comments to clarify the purpose of the empty elements.
Rewrap entries to a single line to have a consistent style.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Acked-by: Florian Fainelli <f.fainelli@gmail.com> [ahci_brcm]
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>