drm/edid: use struct edid * in drm_do_get_edid()

Mixing u8 * and struct edid * is confusing, switch to the latter.

v2:
- Rebase on the invalid block filtering fix
- Rename struct edid *base to *dest_block for clarity (Ville)

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/18bf820c1d20e616076b3275627e7ebf01bce7a3.1648752228.git.jani.nikula@intel.com