docs: dt: rockchip,dwc3.txt: fix a pointer to a renamed file

phy-rockchip-inno-usb2.txt was converted to yaml.

Fix the corresponding reference.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>