Cosmetics: replace "filename" to "arg" for the name of the argument of

opt_input_file(). More consistent and more clear, as "filename" can be
easily confused with the global "input_filename".

Originally committed as revision 22045 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffprobe.c

@@ -288,15 +288,15 @@ static void opt_format(const char *arg)
     }
 }
 
-static void opt_input_file(const char *filename)
+static void opt_input_file(const char *arg)
 {
     if (input_filename) {
-        fprintf(stderr, "Input filename already specified: %s\n", filename);
+        fprintf(stderr, "Input filename already specified: %s\n", arg);
         exit(1);
     }
-    if (!strcmp(filename, "-"))
-        filename = "pipe:";
-    input_filename = filename;
+    if (!strcmp(arg, "-"))
+        arg = "pipe:";
+    input_filename = arg;
 }
 
 static void show_help(void)