Delete typo in SurfaceFlinger documentation

Test: None (this is a comment)
Change-Id: I0876a40697fe5bb5245513520bc1f9a4bf1139f7
diff --git a/services/surfaceflinger/Layer.h b/services/surfaceflinger/Layer.h
index e2b2a3a..0efdf54 100644
--- a/services/surfaceflinger/Layer.h
+++ b/services/surfaceflinger/Layer.h
@@ -707,7 +707,7 @@
 
     // A layer can be attached to multiple displays when operating in mirror mode
     // (a.k.a: when several displays are attached with equal layerStack). In this
-    // case we need to keep track. In non-mirror mode, a layer will have only one.
+    // case we need to keep track. In non-mirror mode, a layer will have only one
     // HWCInfo. This map key is a display layerStack.
     std::unordered_map<int32_t, HWCInfo> mHwcLayers;