Rename const to kFrameTimelinesCapacity

From `kFrameTimelinesLength`.

Bug: 270612751
Test: build
Change-Id: I83e61a19254ab4a63479a2004124cfd2c082da35
diff --git a/libs/gui/VsyncEventData.cpp b/libs/gui/VsyncEventData.cpp
index 91fc9c0..8e00c2f 100644
--- a/libs/gui/VsyncEventData.cpp
+++ b/libs/gui/VsyncEventData.cpp
@@ -23,8 +23,8 @@
 
 namespace android::gui {
 
-static_assert(VsyncEventData::kFrameTimelinesLength == 7,
-              "Must update value in DisplayEventReceiver.java#FRAME_TIMELINES_LENGTH (and here)");
+static_assert(VsyncEventData::kFrameTimelinesCapacity == 7,
+              "Must update value in DisplayEventReceiver.java#FRAME_TIMELINES_CAPACITY (and here)");
 
 int64_t VsyncEventData::preferredVsyncId() const {
     return frameTimelines[preferredFrameTimelineIndex].vsyncId;