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

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'

Cc: stable <stable@vger.kernel.org>
Signed-off-by: NPeter Chen <peter.chen@nxp.com>
Signed-off-by: NMathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/xhci-mem.c

@@ -1724,7 +1724,7 @@ static int scratchpad_alloc(struct xhci_hcd *xhci, gfp_t flags)
 	xhci->dcbaa->dev_context_ptrs[0] = cpu_to_le64(xhci->scratchpad->sp_dma);
 	for (i = 0; i < num_sp; i++) {
 		dma_addr_t dma;
-		void *buf = dma_alloc_coherent(dev, xhci->page_size, &dma,
+		void *buf = dma_zalloc_coherent(dev, xhci->page_size, &dma,
 				flags);
 		if (!buf)
 			goto fail_sp4;