xhci: fix integer overflow

xhci: fix integer overflow

xhci_service_interval_to_ns() returns long long
to avoid an overflow. However, the type cast happens
too late. The fix is to force ULL from the beginning.

This patch should be backported to kernels as old as 3.5, that contain
the commit 46e49d57b3683ff08c7a22ca2408792b083007f3 "xhci: Add Intel
U1/U2 timeout policy."

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
CC: stable@vger.kernel.org