drm/sti: hda: pass const struct drm_display_mode* to hda_get_mode_idx()

Make hda_get_mode_idx() take a const struct drm_display_mode pointer
instead of just raw struct drm_display_mode. This is a preparation to
converting the mode_valid() callback of drm_connector to take a const
struct drm_display_mode argument.

Acked-by: Raphael Gallais-Pou <rgallaispou@gmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241214-drm-connector-mode-valid-const-v2-3-4f9498a4c822@linaro.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>