drm/amd/display: Catch errors from drm_atomic_helper_suspend()

drm_atomic_helper_suspend() can return PTR_ERR(), in which case the
error gets stored into `dm->cached_state`.  This can cause failures
during resume.  Catch the error during suspend and fail the suspend
instead.

Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2362


Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>