OWNERS: add Thu Nguyen for Ampere-specific files

Add `Thu Nguyen <thu@os.amperecomputing.com>` as an owner/reviewer on
any files in a Ampere sub-directory, such as `oem/ampere/`.

Signed-off-by: Thu Nguyen <thu@os.amperecomputing.com>
Change-Id: Ib57af2281e3837ff265ab7589f6451fa7279be2d
diff --git a/OWNERS b/OWNERS
index 162f7ac..b70ba46 100644
--- a/OWNERS
+++ b/OWNERS
@@ -42,6 +42,9 @@
 - thu@os.amperecomputing.com
 
 matchers:
+- partial_regex: ampere
+  owners:
+  - thu@os.amperecomputing.com
 - partial_regex: ibm
   owners:
   - manojkiran.eda@gmail.com