drm/edid: Use block local to refer to the block

Now that we have the name "block" free once more, we can use it to point
to the start of a block within the edid.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161017083514.21772-2-chris@chris-wilson.co.uk