xhci-plat: Update IRQ flag for primary HCD

Commit bb2195e5 ("usb: dwc3: Change dwc3 irq to oneshot threaded
irq") updated IRQ flag with IRQF_ONESHOT with USB XHCI platform driver
but it missed updating this with primary HCD. This results into
mismatch of IRQ flag with XHCI and USB DWC3 causing xhci_probe() failure.
Fix this issue by updating IRQ flag with IRQF_ONESHOT.

CRs-Fixed: 1086141
Change-Id: Icc276c7cc38a8b8b8ec12835d7caf7c2e7003083
Signed-off-by: Mayank Rana <mrana@codeaurora.org>