xhci: Remove excessive printks with shared IRQs.

If the xHCI host controller shares an interrupt line with another device,
the xHCI driver needs to check if the interrupt was generated by its
hardware.  Unfortunately, the user will see a ton of "Spurious interrupt."
lines if the other hardware interrupts often.  Lawrence found his dmesg
output cluttered with this output when the xHCI host shared an interrupt
with his i915 hardware.

Remove the warning, as sharing an interrupt is a normal thing.

This should be applied to the 2.6.36 stable tree.
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Reported-by: Lawrence Rust <lvr@softsystem.co.uk>
Cc: stable@kernel.org

drivers/usb/host/xhci-ring.c

@@ -2104,7 +2104,6 @@ irqreturn_t xhci_irq(struct usb_hcd *hcd)
 
 	if (!(status & STS_EINT)) {
 		spin_unlock(&xhci->lock);
-		xhci_warn(xhci, "Spurious interrupt.\n");
 		return IRQ_NONE;
 	}
 	xhci_dbg(xhci, "op reg status = %08x\n", status);