usb: phy: msm: Use usb_add_phy_dev() to register device

There could be more than one USB2.0 PHY's on the platform.
This will allow all of them to be registered successfully.

Signed-off-by: Ivan T. Ivanov <iivanov@mm-sol.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>