drm: fix code style for embedded structs in hdr_metadata_infoframe

Only the stuff inside the brackets should be indented.
Signed-off-by: Simon Ser <contact@emersion.fr>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Sebastian Wick <sebastian.wick@redhat.com>
Cc: Joshua Ashton <joshua@froggi.es>
Cc: Pekka Paalanen <pekka.paalanen@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230428100115.9802-1-contact@emersion.fr