drm: bridge: it66121: Use regmap_noinc_read()

Use regmap_noinc_read() instead of reading the data from the DDC FIFO one
byte at a time.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20221214125821.12489-4-paul@crapouillou.net