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>
Link: https://lore.kernel.org/r/287bd271f5c542e9d12a132a6b6a17672c9fd67c.1586881715.git.mchehab+huawei@kernel.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>