drm/msm/dp: add a missing unlock in dp_hpd_plug_handle()

drm/msm/dp: add a missing unlock in dp_hpd_plug_handle()

When pm_runtime_resume_and_get() fails, unlock before returning.

Fixes: 5814b8bf086a ("drm/msm/dp: incorporate pm_runtime framework into DP driver")
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/570395/
Link: https://lore.kernel.org/r/20231204171317.192427-1-harshit.m.mogalapalli@oracle.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>