display: Fix acquireFenceFd memory leak

Remove return statement from display commit failure and assign
the return value as -1 to avoid memory leak during error scenario.

Change-Id: I87dd73e997e016f89944bb1603b517847bbc555c
diff --git a/libhwcomposer/hwc.cpp b/libhwcomposer/hwc.cpp
index 7398295..8064ef4 100644
--- a/libhwcomposer/hwc.cpp
+++ b/libhwcomposer/hwc.cpp
@@ -388,7 +388,7 @@
 
         if (display_commit(ctx, dpy) < 0) {
             ALOGE("%s: display commit fail!", __FUNCTION__);
-            return -1;
+            ret = -1;
         }
     }