usb: host: Fix passing of core-id property to xhci-plat

xhci-plat probe expects to read any device tree based configuration
specific to dwc3 updated from dwc3 controller software. Hence read
usb-core-id property from dwc3's probe, and updates as usb-core-id
property with xhci device. Also use xhci device (i.e. &pdev->dev)
instead of dwc3 (i.e. sysdev) with xhci-plat probe to read updated
usb-core-id value.

Change-Id: If7f1f6aede48b2181a22ccdbad33474255cc6d11
Signed-off-by: Mayank Rana <mrana@codeaurora.org>