dt-bindings: gpio: Add Sergey Semin to DW APB GPIO driver maintainers

Seeing Hoan has been silent for a long time Linus suggested to me
to be also maintaining the driver. This patch adds myself to the list
of maintainers in the DT schema of the driver.

Suggested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Cc: Hoan Tran <hoan@os.amperecomputing.com>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Paul Burton <paulburton@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Link: https://lore.kernel.org/r/20200323195401.30338-4-Sergey.Semin@baikalelectronics.ru


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>