vp9_noise_estimate.c: make function static

enable_noise_estimation() is local to this module

Change-Id: Id736c419387ca1959695dd327ce164bec029b597

vp9/encoder/vp9_noise_estimate.c

diff --git a/vp9/encoder/vp9_noise_estimate.c b/vp9/encoder/vp9_noise_estimate.c
index c3351af..212a76d 100644
--- a/vp9/encoder/vp9_noise_estimate.c
+++ b/vp9/encoder/vp9_noise_estimate.c
@@ -39,7 +39,7 @@
   ne->num_frames_estimate = 20;
 }
 
-int enable_noise_estimation(VP9_COMP *const cpi) {
+static int enable_noise_estimation(VP9_COMP *const cpi) {
   // Enable noise estimation if denoising is on.
 #if CONFIG_VP9_TEMPORAL_DENOISING
   if (cpi->oxcf.noise_sensitivity > 0)