MAINTAINERS: update ti,omap-gpio.yaml reference

Changeset bc3aca53 ("dt-bindings: gpio: omap: Convert to json-schema")
renamed: Documentation/devicetree/bindings/gpio/gpio-omap.txt
to: Documentation/devicetree/bindings/gpio/ti,omap-gpio.yaml.

Update its cross-reference accordingly.

Fixes: bc3aca53

 ("dt-bindings: gpio: omap: Convert to json-schema")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>