Revert patch string from 2017-04-05 to 2017-04-01

Change-Id: I64d0abaa33c186c7fb00035f499451cd8e8ee6f8
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 86a67a1..9d67166 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -114,7 +114,7 @@
     #  It must be of the form "YYYY-MM-DD" on production devices.
     #  It must match one of the Android Security Patch Level strings of the Public Security Bulletins.
     #  If there is no $PLATFORM_SECURITY_PATCH set, keep it empty.
-      PLATFORM_SECURITY_PATCH := 2017-04-05
+      PLATFORM_SECURITY_PATCH := 2017-04-01
 endif
 
 ifeq "" "$(PLATFORM_BASE_OS)"