MAINTAINERS: Change my role from Maintainer to Reviewer

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Rodrigo Siqueira <siqueira@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 9b3ef540)
Cc: stable@vger.kernel.org