usb: dwc3: rockchip: Fix PHY documentation links.

Commit 34962fb8 ("docs: Fix more broken references") replaced the
broken reference to rockchip,dwc3-usb-phy.txt binding for the Qualcomm
DWC3 binding (qcom-dwc3-usb-phy.txt). That's wrong, so replace that
reference for the correct ones.

Fixes: 34962fb8

 ("docs: Fix more broken references")
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>