drm/edid: make drm_edid_header_is_valid() accept void pointer

It will be useful to accept a struct edid *, but for compatibility with
existing usage accept void *.

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/33fbe1615a3bd82112eaf4077bbb521793cbb91a.1648752228.git.jani.nikula@intel.com