drm/bridge/sii8620: remove HSIC initialization

HSIC initialization was taken from the vendor code. HSIC in MHL circuit
is not connected, so it is not possible to test it. Tests prove that
without HSIC the device works well. Therefore it can be removed.

Signed-off-by: Maciej Purski <m.purski@samsung.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1511968368-30884-1-git-send-email-m.purski@samsung.com