drm/bridge: sii902x: Fix mode_valid hook

drm/bridge: sii902x: Fix mode_valid hook

Currently, mode_valid is defined only in drm_connector_helper_funcs.
When the bridge is attached with the 'DRM_BRIDGE_ATTACH_NO_CONNECTOR'
flag, the connector is not initialized, and so is the mode_valid
hook under connector helper funcs.
It also returns MODE_OK for all modes without actually checking the
modes.
So move the mode_valid hook to drm_bridge_funcs with proper clock
checks for maximum and minimum pixel clock supported by the bridge.

Signed-off-by: Jayesh Choudhary <j-choudhary@ti.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Acked-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Reviewed-by: Aradhya Bhatia <a-bhatia1@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240613083805.439337-2-j-choudhary@ti.com
Signed-off-by: Maxime Ripard <mripard@kernel.org>