drm/edid: Kerneldoc for newly added edid_corrupt

Also treat it as a proper boolean.

Cc: Todd Previte <tprevite@gmail.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>