phy: rockchip: usbdp: fix uninitialized variable

The ret variable may not be initialized in rk_udphy_usb3_phy_init(), if
the PHY is not using USB3 mode.

Since the DisplayPort part is handled separately and the PHY does not
support USB2 (which is routed to another PHY on Rockchip RK3588), the
right exit code for this case is 0. Thus let's initialize the variable
accordingly.

Fixes: 2f70bbddeb457 ("phy: rockchip: add usbdp combo phy driver")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202404141048.qFAYDctQ-lkp@intel.com/
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Link: https://lore.kernel.org/r/20240416145233.94687-1-sebastian.reichel@collabora.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

phy: rockchip: add usbdp combo phy driver

This adds a new USBDP combo PHY with Samsung IP block driver.

The driver get lane mux and mapping info in 2 ways, supporting
DisplayPort alternate mode or parsing from DT. When parsing from DT,
the property "rockchip,dp-lane-mux" provide the DP mux and mapping
info. This is needed when the PHY is not used with TypeC Alt-Mode.
For example if the USB3 interface of the PHY is connected to a USB
Type A connector and the DP interface is connected to a DisplayPort
connector.

When do DP link training, need to set lane number, link rate, swing,
and pre-emphasis via PHY configure interface.

Co-developed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Co-developed-by: Zhang Yubing <yubing.zhang@rock-chips.com>
Signed-off-by: Zhang Yubing <yubing.zhang@rock-chips.com>
Co-developed-by: Frank Wang <frank.wang@rock-chips.com>
Signed-off-by: Frank Wang <frank.wang@rock-chips.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20240408225109.128953-3-sebastian.reichel@collabora.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>