Move lastfm resource pool to base

MediaBrowser.Controller/Providers/Music/LastfmArtistProvider.cs

@@ -18,7 +18,6 @@ namespace MediaBrowser.Controller.Providers.Music
 {
     public class LastfmArtistProvider : LastfmBaseArtistProvider
     {
-        internal readonly SemaphoreSlim LastfmResourcePool = new SemaphoreSlim(5, 5);
 
         public LastfmArtistProvider(IJsonSerializer jsonSerializer, IHttpClient httpClient, ILogManager logManager, IServerConfigurationManager configurationManager)
             : base(jsonSerializer, httpClient, logManager, configurationManager)

MediaBrowser.Controller/Providers/Music/LastfmBaseProvider.cs

@@ -24,6 +24,8 @@ namespace MediaBrowser.Controller.Providers.Music
     /// </summary>
     public abstract class LastfmBaseProvider : BaseMetadataProvider
     {
+        protected static readonly SemaphoreSlim LastfmResourcePool = new SemaphoreSlim(5, 5);
+
         /// <summary>
         /// Initializes a new instance of the <see cref="LastfmBaseProvider" /> class.
         /// </summary>