xhci: Allocate correct amount of scratchpad buffers

Include the high order bit fields for Max scratchpad buffers when
calculating how many scratchpad buffers are needed.

I'm suprised this hasn't caused more issues, we never allocated more than
32 buffers even if xhci needed more. Either we got lucky and xhci never
really used past that area, or then we got enough zeroed dma memory anyway.

Should be backported as far back as possible

Reported-by: Tim Chen <tim.c.chen@linux.intel.com>
Tested-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>