drm/bridge: sii9234: silence warning about regulators during deferred probe

Don't confuse user with meaningless warning about failure in getting
regulators in case of deferred probe.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200226101307.16708-1-m.szyprowski@samsung.com