vf_hwupload: Add missing return value check

Add missing return value checks to suppress build warning and
remove noop ff_formats_unref() calling.

Note: most filters using ff_formats_ref() didn't have a suitable
error handling, it's a potential memory leak issue.

Signed-off-by: Jun Zhao <jun.zhao@intel.com>
Signed-off-by: Mark Thompson <sw@jkqxz.net>