pinctrl: renesas: rza2: Mark GPIOs as used

GPIOs showed up as unclaimed in debugfs, so they could be muxed to
something else even though they were in use.  Mark GPIOs as claimed when
in use to avoid that.

Reported-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/2862093f7701dcaf29f37c0b2f9268234168338f.1727711124.git.geert+renesas@glider.be