Update get_maximum_overview_level to use Rasterio dataset directly

[vincentsarago]

in

rio-cogeo/rio_cogeo/cogeo.py

Lines 62 to 66 in fb9ceba

	if overview_level is None:
	overview_level = get_maximum_overview_level(
	src_path, min(int(dst_kwargs["blockxsize"]), int(dst_kwargs["blockysize"]))
	)

we pass the dataset path and then open it in get_maximum_overview_level function. This means we have to open the dataset twice while it's not really necessary