usb: host: xhci: delete sp_dma_buffers for scratchpad

We already have sp_array to store each scratch buffer address for xHC,
it doesn't need another sp_dma_buffers array to store it.

Signed-off-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>