drm/bridge/sii8620: fix loops in EDID fetch logic

Function should constantly check if cable is connected and finish
in finite time.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Maciej Purski <m.purski@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180115173357.31067-4-a.hajda@samsung.com