drm: bridge: adv7511: fix CEC power down control register offset

The ADV7511_REG_CEC_CTRL = 0xE2 register is part of the main register
map - not the CEC register map. As such, we shouldn't apply an offset to
the register address. Doing so will cause us to address a bogus register
for chips with a CEC register map offset (e.g. ADV7533).

Fixes: 3b1b9750 ("drm: adv7511/33: add HDMI CEC support")
Signed-off-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220612144854.2223873-2-alvin@pqrs.dk