usb: xhci: Add error handling in xhci_map_urb_for_dma

In the Linux kernel, the following vulnerability has been resolved:

usb: xhci: Add error handling in xhci_map_urb_for_dma

Currently xhci_map_urb_for_dma() creates a temporary buffer and copies

the SG list to the new linear buffer. But if the kzalloc_node() fails,

then the following sg_pcopy_to_buffer() can lead to crash since it

tries to memcpy to NULL pointer.

So return -ENOMEM if kzalloc returns null pointer.