drm/bridge: it6505: Add i2c api power on check

Use i2c bus to read/write when it6505 power off will occur i2c error.
Add this check will prevent i2c error when it6505 power off.

Signed-off-by: Pin-Yen Lin <treapking@chromium.org>
Signed-off-by: Allen Chen <allen.chen@ite.com.tw>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220715024910.12578-3-allen.chen@ite.com.tw