MAINTAINERS: rectify entry for MICROCHIP USB251XB DRIVER

Commit fff61d4c ("dt-bindings: usb: usb251xb: Convert to YAML schema")
converts usb251xb.txt to usb251xb.yaml, but misses to adjust its reference
in MAINTAINERS.

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

Repair this file reference in MICROCHIP USB251XB DRIVER.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Acked-by: Marek Vasut <marex@denx.de>
Link: https://lore.kernel.org/r/20221115103153.28502-1-lukas.bulwahn@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

MAINTAINERS

@@ -13644,7 +13644,7 @@ MICROCHIP USB251XB DRIVER
 M:	Richard Leitner <richard.leitner@skidata.com>
 L:	linux-usb@vger.kernel.org
 S:	Maintained
-F:	Documentation/devicetree/bindings/usb/usb251xb.txt
+F:	Documentation/devicetree/bindings/usb/usb251xb.yaml
 F:	drivers/usb/misc/usb251xb.c
 
 MICROCHIP USBA UDC DRIVER