usb: xhci: Remove usb_phy get phandle from xhci_plat_probe

usb_phy_init will be called as a part of core_reset.
Adding usb_phy phandle in xhci_plat_probe will call
usb_phy_init twice which is breaking host mode
functionality. This change removes usb_phy get
phandle from xhci_plat_probe.

Change-Id: Ib407bf1d108cb030fd9c8ab71000127ae305b955
Signed-off-by: Pratham Pratap <prathampratap@codeaurora.org>