Set the Security Patch level for MNC

MNC will include the security patches from the August OEM bulletin
which will have a patch date of September 1.

Bug: 23288951
Change-Id: Ia0f313bf35fa7af1efed1787006bfbb614bc8c29
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 483c8f2..691a4bd 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -103,7 +103,7 @@
   # Can be an arbitrary string, but must be a single word.
   #
   # If there is no $PLATFORM_SECURITY_PATCH set, keep it empty.
-  PLATFORM_SECURITY_PATCH :=
+  PLATFORM_SECURITY_PATCH := 2015-09-01
 endif
 
 ifeq "" "$(PLATFORM_BASE_OS)"