Move OWNER reference master=>main.

BUG=b/291759353

Change-Id: I98a997ca6af68ad66d30d49e6998483840f88408
diff --git a/OWNERS b/OWNERS
index e58fb39..f37daeb 100644
--- a/OWNERS
+++ b/OWNERS
@@ -1,2 +1,2 @@
 set noparent
-file:platform/system/bpf:master:/OWNERS_bpf
+file:platform/system/bpf:main:/OWNERS_bpf