dt-bindings: w1: update w1-gpio.yaml reference

Changeset dd2c898b ("dt-bindings: w1: Convert 1-Wire GPIO binding to a schema")
renamed: Documentation/devicetree/bindings/w1/w1-gpio.txt
to: Documentation/devicetree/bindings/w1/w1-gpio.yaml.

Update its cross-reference accordingly.

Fixes: dd2c898b ("dt-bindings: w1: Convert 1-Wire GPIO binding to a schema")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/0b415b5e05bcf9d593cb421c96996d914528e732.1631785820.git.mchehab+huawei@kernel.org