drm/edid: restore some type safety to cea_db_*() functions

During the transition, we accepted a void pointer for a poor C
programmer's version of polymorphism. Switch the functions to use struct
cea_db * to regain some more type safety.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/c6ad496cdadea1bb598711a65ef536f4a43b74a7.1651569697.git.jani.nikula@intel.com