USB: xhci: Fix scratchpad deallocation.

The scratchpad_free() function uses xhci->page_size to free some memory
with pci_free_consistent().  However, the page_size is set to zero before
the call, causing kernel oopses on driver unload.  Call scratchpad_free()
before setting xhci->page_size to zero.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Acked-by: John Youn <John.Youn@synopsys.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>