Skip duplicate denoiser frame buffer allocation

Allocate the frame buffer allocation for denoiser once during the
encoder initialization. This avoids allocating frame buffer
multiple times and overwriting the buffer pointer without proper
releasing.

Change-Id: I9b3baa6283449d86fd164534d344c036bb035700

vp9/encoder/vp9_denoiser.c

@@ -458,12 +458,14 @@ int vp9_denoiser_alloc(VP9_DENOISER *denoiser, int width, int height,
   make_grayscale(&denoiser->running_avg_y[i]);
 #endif
   denoiser->increase_denoising = 0;
+  denoiser->frame_buffer_initialized = 1;
 
   return 0;
 }
 
 void vp9_denoiser_free(VP9_DENOISER *denoiser) {
   int i;
+  denoiser->frame_buffer_initialized = 0;
   if (denoiser == NULL) {
     return;
   }