xhci: Use correct SLOT ID when handling a reset device command

Command completion events normally include command completion status,
SLOT_ID, and a pointer to the original command. Reset device command
completion SLOT_ID may be zero according to xhci specs 4.6.11.

VIA controllers set the SLOT_ID to zero, triggering a WARN_ON in the
command completion handler.

Use the SLOT ID found from the original command instead.

This patch should be applied to stable kernels since 3.13 that contain
the commit 20e7acb1


"xhci: use completion event's slot id rather than dig it out of command"

Cc: stable@vger.kernel.org # 3.13
Reported-by: Saran Neti <sarannmr@gmail.com>
Tested-by: Saran Neti <sarannmr@gmail.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>