phy: qualcomm: ipq806x-usb: Fix kernel-doc style

The functions are documented but there were style issues, so fix
the style and add missing description for phy_dwc3

drivers/phy/qualcomm/phy-qcom-ipq806x-usb.c:130:
drivers/phy/qualcomm/phy-qcom-ipq806x-usb.c:174:
drivers/phy/qualcomm/phy-qcom-ipq806x-usb.c:212: warning:
This comment starts with '/**', but isn't a kernel-doc comment.
Refer Documentation/doc-guide/kernel-doc.rst

Signed-off-by: Vinod Koul <vkoul@kernel.org>