Add myself as a maintainer

This repository has a fairly large backlog of reviews, and I'd like to
help out.  I've made changes to the codebase before and I've also been
an active maintainer for other repositories for several years.

I don't meet the new requirements put out in the docs repo, but EM has a
fairly small and mostly stable codebase already. Most of the reviews are
for the JSON configuration files that define cards.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I0c21096f4b7e3b0ffdc7e8a2b5ac6c4d4f2e5dd6
diff --git a/OWNERS b/OWNERS
index 65a6a47..29ccc0d 100644
--- a/OWNERS
+++ b/OWNERS
@@ -33,6 +33,7 @@
 
 owners:
 - ed@tanous.net
+- spinler@us.ibm.com
 - vernon.mauery@linux.intel.com
 - zhikui.ren@intel.com
 
@@ -44,6 +45,9 @@
 - name: Ed Tanous
   email: ed@tanous.net
   discord: edtanous
+- name: Matt Spinler
+  email: spinler@us.ibm.com
+  discord: mspinler
 - name: Vernon Mauery
   email: vernon.mauery@linux.intel.com
   discord: vmauery