iio: adc: Fix Renesas GyroADC MAINTAINERS entry

Fix the F: entry in MAINTAINERS file, point it to the correct file.
While at it, add DT binding doc F: entry too.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Joe Perches <joe@perches.com>
Cc: linux-renesas-soc@vger.kernel.org
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>