drm/edid: add single point of return to drm_do_get_edid()

This will be useful in the future. Use fail label for fail exit.

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/8e564e9415baa4dc9dc3127e4200b2618a8a3ba0.1649685475.git.jani.nikula@intel.com