MAINTAINERS: rectify entry for XILINX GPIO DRIVER

Commit ba96b2e7 ("dt-bindings: gpio: gpio-xilinx: Convert Xilinx axi
gpio binding to YAML") converts gpio-xilinx.txt to xlnx,gpio-xilinx.yaml,
but missed to adjust its reference in MAINTAINERS.

Hence, ./scripts/get_maintainer.pl --self-test=patterns complains about a
broken reference.

Repair this file reference in XILINX GPIO DRIVER.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>

MAINTAINERS

@@ -22301,7 +22301,7 @@ M:	Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
 R:	Srinivas Neeli <srinivas.neeli@xilinx.com>
 R:	Michal Simek <michal.simek@xilinx.com>
 S:	Maintained
-F:	Documentation/devicetree/bindings/gpio/gpio-xilinx.txt
+F:	Documentation/devicetree/bindings/gpio/xlnx,gpio-xilinx.yaml
 F:	Documentation/devicetree/bindings/gpio/gpio-zynq.yaml
 F:	drivers/gpio/gpio-xilinx.c
 F:	drivers/gpio/gpio-zynq.c