drm/msm: loop over encoders using drm_for_each_encoder()

Rather than manually looping over encoders array, use standard
drm_for_each_encoder() macro.

Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/480942/
Link: https://lore.kernel.org/r/20220406101247.483649-3-dmitry.baryshkov@linaro.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>