MAINTAINERS: add Takahiro Kuwano as SPI NOR reviewer

Takahiro has been an active contributor to the SPI NOR subsystem,
providing valuable patches and reviews. Add him as a designated
reviewer to help facilitate patch processing and maintenance.

Cc: Takahiro Kuwano <takahiro.kuwano@infineon.com>
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Acked-by: Takahiro Kuwano <takahiro.kuwano@infineon.com>
Acked-by: Michael Walle <mwalle@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>