avfilter/vf_premultiply: Fix leak of names of inpads

These names leak because freeing them in the uninit function has been
forgotten. Instead of adding the freeing code, this commit stops
allocating these names. They are constants anyway.

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavfilter/vf_premultiply.c

@@ -673,27 +673,19 @@ static av_cold int init(AVFilterContext *ctx)
         s->inverse = 1;
 
     pad.type         = AVMEDIA_TYPE_VIDEO;
-    pad.name         = av_strdup("main");
+    pad.name         = "main";
     pad.config_props = config_input;
-    if (!pad.name)
-        return AVERROR(ENOMEM);
 
-    if ((ret = ff_insert_inpad(ctx, 0, &pad)) < 0) {
-        av_freep(&pad.name);
+    if ((ret = ff_insert_inpad(ctx, 0, &pad)) < 0)
         return ret;
-    }
 
     if (!s->inplace) {
         pad.type         = AVMEDIA_TYPE_VIDEO;
-        pad.name         = av_strdup("alpha");
+        pad.name         = "alpha";
         pad.config_props = NULL;
-        if (!pad.name)
-            return AVERROR(ENOMEM);
 
-        if ((ret = ff_insert_inpad(ctx, 1, &pad)) < 0) {
-            av_freep(&pad.name);
+        if ((ret = ff_insert_inpad(ctx, 1, &pad)) < 0)
             return ret;
-        }
     }
 
     return 0;