MAINTAINERS: update Sampa to match Gerrit

The previous email address listed for Sampa is not
found in Gerrit, which breaks the tooling used to
automatically assign reviewers using the MAINTAINERS
file.  Update per Gerrit userid.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ia5ee16804050e4037b06b6ff9680cb4b6ea88a28