drm/tinydrm: Embed the mode in tinydrm_connector

Embed the mode in tinydrm_connector instead of doing an devm_ allocation.
Remove unnecessary use of ret variable at the end of
tinydrm_display_pipe_init().

Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: David Lechner <david@lechnology.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180110185940.53841-7-noralf@tronnes.org