drm/msm/dp: fix runtime PM leak on disconnect

drm/msm/dp: fix runtime PM leak on disconnect

Make sure to put the runtime PM usage count (and suspend) also when
receiving a disconnect event while in the ST_MAINLINK_READY state.

This specifically avoids leaking a runtime PM usage count on every
disconnect with display servers that do not automatically enable
external displays when receiving a hotplug notification.

Fixes: 5814b8bf086a ("drm/msm/dp: incorporate pm_runtime framework into DP driver")
Cc: stable@vger.kernel.org      # 6.8
Cc: Kuogee Hsieh <quic_khsieh@quicinc.com>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/582744/
Link: https://lore.kernel.org/r/20240313164306.23133-2-johan+linaro@kernel.org
Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>