MAINTAINERS: update gpio-zynq.yaml reference

Changeset 45ca16072b70 ("dt-bindings: gpio: zynq: convert bindings to YAML")
renamed: Documentation/devicetree/bindings/gpio/gpio-zynq.txt
to: Documentation/devicetree/bindings/gpio/gpio-zynq.yaml.

Update its cross-reference accordingly.

Fixes: 45ca16072b70 ("dt-bindings: gpio: zynq: convert bindings to YAML")
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>
Signed-off-by: Bartosz Golaszewski <[e-mail]>

MAINTAINERS

···
 R:	Michal Simek <[e-mail]>
 S:	Maintained
 F:	Documentation/devicetree/bindings/gpio/gpio-xilinx.txt
-F:	Documentation/devicetree/bindings/gpio/gpio-zynq.txt
+F:	Documentation/devicetree/bindings/gpio/gpio-zynq.yaml
 F:	drivers/gpio/gpio-xilinx.c
 F:	drivers/gpio/gpio-zynq.c