hammerhead: update prebuilt kernel

2d91c66 hammerhead: turn off /dev/mem /dev/kmem
bebb36b idr: fix a subtle bug in idr_get_next()

Linux version 3.4.0-g2d91c66 (android-build@vpbs1.mtv.corp.google.com)
(gcc version 4.7 (GCC) ) #1 SMP PREEMPT Tue Mar 10 18:10:05 UTC 2015

Bug: 19549480
Bug: 19665182
Bug: 18069309
Bug: 19236185

Change-Id: Ie6ef994817c53a6f139564d6fcf4d3d634dae013
Signed-off-by: Patrick Tjin <pattjin@google.com>
diff --git a/zImage-dtb b/zImage-dtb
index 4705d07..d27c2e9 100755
--- a/zImage-dtb
+++ b/zImage-dtb
Binary files differ