drm/connector: Rename subconnector state variable

drm/connector: Rename subconnector state variable

There is two TV subconnector related properties registered by
drm_mode_create_tv_properties(): subconnector and select subconnector.

While the select subconnector property is stored in the kernel by the
drm_tv_connector_state structure, the subconnector property isn't stored
anywhere.

Worse, the select subconnector property is stored in a field called
subconnector, creating some ambiguity about which property content we're
accessing.

Let's rename that field to one called select_subconnector to make it move
obvious what it's about.

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://lore.kernel.org/r/20220728-rpi-analog-tv-properties-v4-5-60d38873f782@cerno.tech
Signed-off-by: Maxime Ripard <maxime@cerno.tech>