sdm: Set refresh rate only if there is a change

Set refresh rate only when needed, without this we
are reconfiguring display in every composition cycle.

Change-Id: I612e5184c8e88ed63f9a559ea8c5962b0d64a5d1
diff --git a/sdm/libs/hwc/hwc_display_primary.cpp b/sdm/libs/hwc/hwc_display_primary.cpp
index 569fc0f..5cf1b56 100755
--- a/sdm/libs/hwc/hwc_display_primary.cpp
+++ b/sdm/libs/hwc/hwc_display_primary.cpp
@@ -113,6 +113,7 @@
 
 int HWCDisplayPrimary::Prepare(hwc_display_contents_1_t *content_list) {
   int status = 0;
+  DisplayError error = kErrorNone;
 
   if (!boot_animation_completed_)
     ProcessBootAnimCompleted();
@@ -136,7 +137,10 @@
   ToggleCPUHint(one_updating_layer);
 
   uint32_t refresh_rate = GetOptimalRefreshRate(one_updating_layer);
-  DisplayError error = display_intf_->SetRefreshRate(refresh_rate);
+  if (current_refresh_rate_ != refresh_rate) {
+    error = display_intf_->SetRefreshRate(refresh_rate);
+  }
+
   if (error == kErrorNone) {
     // On success, set current refresh rate to new refresh rate
     current_refresh_rate_ = refresh_rate;