drm/i915: Use EIO instead of EAGAIN for sink CRC error.

If something while getting panel CRC this means that probably hw I/O error
so hw is busted and try again shouldn't help much.

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>