drm/msm/dpu: move dpu_encoder's connector assignment to atomic_enable()

drm/msm/dpu: move dpu_encoder's connector assignment to atomic_enable()

For cases where the crtc's connectors_changed was set without enable/active
getting toggled , there is an atomic_enable() call followed by an
atomic_disable() but without an atomic_mode_set().

This results in a NULL ptr access for the dpu_encoder_get_drm_fmt() call in
the atomic_enable() as the dpu_encoder's connector was cleared in the
atomic_disable() but not re-assigned as there was no atomic_mode_set() call.

Fix the NULL ptr access by moving the assignment for atomic_enable() and also
use drm_atomic_get_new_connector_for_encoder() to get the connector from
the atomic_state.

Fixes: 25fdd5933e4c ("drm/msm: Add SDM845 DPU support")
Reported-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Closes: https://gitlab.freedesktop.org/drm/msm/-/issues/59
Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Tested-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org> # SM8350-HDK
Patchwork: https://patchwork.freedesktop.org/patch/606729/
Link: https://lore.kernel.org/r/20240731191723.3050932-1-quic_abhinavk@quicinc.com
Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>