drm/bridge: cadence: cdns-mhdp8546-core: Set the mhdp connector earlier in atomic_enable()

In the Linux kernel, the following vulnerability has been resolved:

drm/bridge: cadence: cdns-mhdp8546-core: Set the mhdp connector earlier in atomic_enable()

In case if we get errors in cdns_mhdp_link_up() or cdns_mhdp_reg_read() in atomic_enable, we will go to cdns_mhdp_modeset_retry_fn() and will hit NULL pointer while trying to access the mutex. We need the connector to be set before that. Unlike in legacy cases with flag !DRM_BRIDGE_ATTACH_NO_CONNECTOR, we do not have connector initialised in bridge_attach(), so add the mhdp->connector_ptr in device structure to handle both cases with DRM_BRIDGE_ATTACH_NO_CONNECTOR and !DRM_BRIDGE_ATTACH_NO_CONNECTOR, set it in atomic_enable() earlier to avoid possible NULL pointer dereference in recovery paths like modeset_retry_fn() with the DRM_BRIDGE_ATTACH_NO_CONNECTOR flag set.