pinctrl: sh-pfc: Remove r8a7791 platform_device_id entry

The r8a7791 platform is now DT-only, the driver doesn't need to match
platform devices by name anymore. Remove the corresponding
platform_device_id entry.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>