Set FFmpeg.AutoGen library search path on Linux

This fix FFmpeg.AutoGen being unable to find system ffmpeg libraries on
Linux.

Ryujinx/Program.cs

@@ -1,4 +1,5 @@
 using ARMeilleure.Translation.PTC;
+using FFmpeg.AutoGen;
 using Gtk;
 using Ryujinx.Common.Configuration;
 using Ryujinx.Common.Logging;
@@ -76,6 +77,9 @@ namespace Ryujinx
             if (OperatingSystem.IsLinux())
             {
                 XInitThreads();
+
+                // Configure FFmpeg search path
+                ffmpeg.RootPath = "/lib";
             }
 
             string systemPath = Environment.GetEnvironmentVariable("Path", EnvironmentVariableTarget.Machine);