core: fix pw_core_find_format() for active ports
Created by: michaelolbrich
pw_core_find_format() is currently broken when one of the ports is already active: The format of the active port is used and the other port is completely ignored. As a result, the autolink module may try to link a new port to the first already active port even if the formats do not match.
To fix this, use the format of the active port as a filter when enumerating the format of the other port.