MAINTAINERS: update st,lsm6dsx.yaml reference

Changeset 7a2cf8e9 ("dt-bindings:iio:imu:st,lsm6dsx: txt to yaml conversion")
renamed: Documentation/devicetree/bindings/iio/imu/st_lsm6dsx.txt
to: Documentation/devicetree/bindings/iio/imu/st,lsm6dsx.yaml.

Update its cross-reference accordingly.

Fixes: 7a2cf8e9 ("dt-bindings:iio:imu:st,lsm6dsx: txt to yaml conversion")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

MAINTAINERS

@@ -16937,7 +16937,7 @@ M:	Lorenzo Bianconi <lorenzo.bianconi83@gmail.com>
 L:	linux-iio@vger.kernel.org
 S:	Maintained
 W:	http://www.st.com/
-F:	Documentation/devicetree/bindings/iio/imu/st_lsm6dsx.txt
+F:	Documentation/devicetree/bindings/iio/imu/st,lsm6dsx.yaml
 F:	drivers/iio/imu/st_lsm6dsx/
 
 ST MIPID02 CSI-2 TO PARALLEL BRIDGE DRIVER