xhci: endianness xhci_calculate_intel_u2_timeout

An le16 is accessed without conversion.

This patch should be backported to kernels as old as 3.5, that contain
the commit e3567d2c "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