drm/drm_connector: Provide short description of param 'supported_colorspaces'

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/drm_connector.c:2215: warning: Function parameter or member 'supported_colorspaces' not described in 'drm_mode_create_hdmi_colorspace_property'
 drivers/gpu/drm/drm_connector.c:2239: warning: Function parameter or member 'supported_colorspaces' not described in 'drm_mode_create_dp_colorspace_property'

Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230824073710.2677348-17-lee@kernel.org


Signed-off-by: Maxime Ripard <mripard@kernel.org>