xhci: fix port BESL LPM capability checking

xhci: fix port BESL LPM capability checking

Wrong capability bit was checked for best effort service latency.
bit 20 indicate port is BESL LPM capable (BLC),
bit 19 is hardware LPM capable (HLC)

This patch should be backported to kernels as old as 3.11, that
contain the commit 4d9b8ae72c9ac2c82dc8ef6826ca65f2b0bf24e1 "usb: xhci:
add USB2 Link power management BESL support"

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Reported-by: Steve Cotton <steve@s.cotton.clara.co.uk>
Cc: stable@vger.kernel.org