external: memset commit struct

Change-Id: I5e6d046f2fdff54fdd58aaca583c0ae8038a9a63
diff --git a/libexternal/external.cpp b/libexternal/external.cpp
index f9ee94c..b9abc31 100644
--- a/libexternal/external.cpp
+++ b/libexternal/external.cpp
@@ -549,7 +549,8 @@
     if(mFd == -1)
         return false;
     struct mdp_display_commit ext_commit;
-    ext_commit.flags |= MDP_DISPLAY_COMMIT_OVERLAY;
+    memset(&ext_commit, 0, sizeof(struct mdp_display_commit));
+    ext_commit.flags = MDP_DISPLAY_COMMIT_OVERLAY;
     if (ioctl(mFd, MSMFB_DISPLAY_COMMIT, &ext_commit) == -1) {
         ALOGE("%s: MSMFB_DISPLAY_COMMIT for external failed, str: %s",
                 __FUNCTION__, strerror(errno));