Add John Stultz to OWNERS

This matches libdrm.

Change-Id: Ifdff3ed4fed349e270801d8810591556328ef85d
diff --git a/OWNERS b/OWNERS
index 3a94bc5..9991fd8 100644
--- a/OWNERS
+++ b/OWNERS
@@ -1,4 +1,5 @@
 adelva@google.com
+john.stultz@linaro.org
 marcheu@google.com
 marissaw@google.com
 seanpaul@google.com