Make process_denoise_mode_change function cond-compiled.

This function is called only when temporal denoising is enabled.

Change-Id: I25a036e3d628edd34410d6e6fe1f9e68a90a8e56

vp8/encoder/onyx_if.c

diff --git a/vp8/encoder/onyx_if.c b/vp8/encoder/onyx_if.c
index 38b8999..74e75c4 100644
--- a/vp8/encoder/onyx_if.c
+++ b/vp8/encoder/onyx_if.c
@@ -3293,6 +3293,7 @@
 
 }
 
+#if CONFIG_TEMPORAL_DENOISING
 static void process_denoiser_mode_change(VP8_COMP *cpi) {
   const VP8_COMMON *const cm = &cpi->common;
   int i, j;
@@ -3399,6 +3400,7 @@
     cpi->denoiser.nmse_source_diff_count = 0;
   }
 }
+#endif
 
 void vp8_loopfilter_frame(VP8_COMP *cpi, VP8_COMMON *cm)
 {