usb: host: Fix passing of xhci-imod-value property to xhci-plat

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

Change-Id: Icf4e903a2f5efb97ae0d0f1de1f880cef536ee6f
Signed-off-by: Mayank Rana <mrana@codeaurora.org>