greybus: loopback: Fix calculations error for ping transfers

For the async ping transfer, statistics are counted twice,
once after the after the gb_loopback_async_operation() and
once in the callback.
Only keep the one in the callback.
Signed-off-by: Alexandre Bailon <abailon@baylibre.com>
Reported-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/loopback.c

@@ -969,7 +969,6 @@ static int gb_loopback_fn(void *data)
 		if (gb->async) {
 			if (type == GB_LOOPBACK_TYPE_PING) {
 				error = gb_loopback_async_ping(gb);
-				gb_loopback_calculate_stats(gb);
 			} else if (type == GB_LOOPBACK_TYPE_TRANSFER) {
 				error = gb_loopback_async_transfer(gb, size);
 			} else if (type == GB_LOOPBACK_TYPE_SINK) {