asf/wtv: use service_provider and service_name metadata tags

Signed-off-by: Ronald S. Bultje <rsbultje@gmail.com>
(cherry picked from commit 45430099438d7b4f70ebb23611a29d318ba49687)

libavformat/asf.c

@@ -153,6 +153,8 @@ const AVMetadataConv ff_asf_metadata_conv[] = {
     { "WM/Tool"            , "encoder"     },
     { "WM/TrackNumber"     , "track"       },
     { "WM/Track"           , "track"       },
+    { "WM/MediaStationCallSign", "service_provider" },
+    { "WM/MediaStationName", "service_name" },
 //  { "Year"               , "date"        }, TODO: conversion year<->date
     { 0 }
 };