xhci: remove unnecessary check in xhci_free_stream_info()

This patch removes the unneccessary check 'if (stream_info)' because
there is already a check few lines above which ensures that stream_info
is not NULL.
Signed-off-by: NXenia Ragiadakou <burzalodowa@gmail.com>
Signed-off-by: NSarah Sharp <sarah.a.sharp@linux.intel.com>

drivers/usb/host/xhci-mem.c

@@ -722,7 +722,6 @@ void xhci_free_stream_info(struct xhci_hcd *xhci,
 				stream_info->stream_ctx_array,
 				stream_info->ctx_array_dma);
 
-	if (stream_info)
 	kfree(stream_info->stream_rings);
 	kfree(stream_info);
 }