drm/edid: add typedef for block read function

Make the callback a bit easier on the eye.

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/10b8721bb7ea8c7df1fd0c1d97c5d446905abbf4.1649685475.git.jani.nikula@intel.com