Move OWNERS entry of ash/webui/conch into ash/OWNERS

Since ash/OWNERS has "set noparent", the original OWNERS entry from
CL:5348956 wasn't effective. Move the entry from root folder OWNERS to
ash/OWNERS instead.

Bug: b:327538047
Change-Id: I7551bcb74439b9ec100ef45545e4bbc6d85fbb4c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5382279
Commit-Queue: Pi-Hsun Shih <pihsun@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1277267}

OWNERS

@@ -38,7 +38,6 @@ per-file README.md=*
 per-file WATCHLISTS=*
 
 # git submodules
-per-file ash/webui/conch=*
 per-file build/fuchsia/internal=*
 per-file chromeos/assistant/internal=*
 per-file clank=*

ash/OWNERS

@@ -17,3 +17,6 @@ per-file BUILD.gn=*
 
 # Translation artifacts:
 per-file ....xtb=file://tools/translation/TRANSLATION_OWNERS
+
+# git submodules
+per-file webui/conch=*