Reset mdns_bridges when at start of find_hue_bridge_mdns().

[itsayellow]

Currently if one calls find_hue_bridge_mdns() multiple times, the same bridge(s) will accumulate in global variable mdns_bridge. Thus calling this function multiple times creates multiple identical (redundant) entries.

This code resets mdns_bridges to an empty list at the beginning of each call of find_hue_bridge_mdns()