usb: host: xhci-plat: Specify IRQF_ONESHOT in irqflag

XHCI driver shares the irq handler with DWC3 device
controller driver which uses IRQF_ONESHOT. For shared
irqs, request_irq requires both the drivers to have
same IRQF_ONESHOT selection, hence update the same.

Change-Id: Id691818d18ca0efaa184190fba306ad4b8a94e55
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>