usb: host: xhci-mem: allocate zeroed Scratchpad Buffer

commit 7480d912 upstream.

According to xHCI ch4.20 Scratchpad Buffers, the Scratchpad
Buffer needs to be zeroed.

	...
	The following operations take place to allocate
       	Scratchpad Buffers to the xHC:
	...
		b. Software clears the Scratchpad Buffer to '0'
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>
[bwh: Backported to 3.2: we only do one allocation for scratchpad buffers]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/usb/host/xhci-mem.c

@@ -1591,7 +1591,7 @@ static int scratchpad_alloc(struct xhci_hcd *xhci, gfp_t flags)
 	if (!xhci->scratchpad)
 		goto fail_sp;
 
-	xhci->scratchpad->sp_array = dma_alloc_coherent(dev,
+	xhci->scratchpad->sp_array = dma_zalloc_coherent(dev,
 				     num_sp * sizeof(u64),
 				     &xhci->scratchpad->sp_dma, flags);
 	if (!xhci->scratchpad->sp_array)