vsrc_buffer: tweak error message in init()

Change:
Expected 7 arguments, but only %d found in '%s'\n
to:
Expected 7 arguments, but %d found in '%s'\n

as the user may provide more than 7 arguments, in that case the error
is not misleading.

libavfilter/vsrc_buffer.c

@@ -120,7 +120,7 @@ static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
         (n = sscanf(args, "%d:%d:%127[^:]:%d:%d:%d:%d", &c->w, &c->h, pix_fmt_str,
                     &c->time_base.num, &c->time_base.den,
                     &c->pixel_aspect.num, &c->pixel_aspect.den)) != 7) {
-        av_log(ctx, AV_LOG_ERROR, "Expected 7 arguments, but only %d found in '%s'\n", n, args);
+        av_log(ctx, AV_LOG_ERROR, "Expected 7 arguments, but %d found in '%s'\n", n, args);
         return AVERROR(EINVAL);
     }
     if ((c->pix_fmt = av_get_pix_fmt(pix_fmt_str)) == PIX_FMT_NONE) {