drm/edid: use EDID block read helper in drm_do_get_edid()

Convert drm_do_get_edit() from the base block read helper to the generic
block read helper. There's quite a bit going on here, as the corrupt and
null EDID information is moved back to the caller. As we see, they were
not all that clear to begin with, and this change underlines that.

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/3bcf98453770757ee93386da0cfbc6552d42a312.1649685475.git.jani.nikula@intel.com