drm/atomic-helper: Don't set deadline for modesets

If the crtc is being switched on or off then the semantics of
computing the timestampe of the next vblank is somewhat ill-defined.
And indeed, the code splats with a warning in the timestamp
computation code. Specifically it hits the check to make sure that
atomic drivers have full set up the timing constants in the drm_vblank
structure, and that's just not the case before the crtc is actually
on.

For robustness it seems best to just not set deadlines for modesets.

v2: Also skip on inactive crtc (Ville)

Link: https://lore.kernel.org/dri-devel/[e-mail]/
Fixes: d39e48ca80c0 ("drm/atomic-helper: Set fence deadline for vblank")
Cc: Ville Syrjälä <[e-mail]>
Cc: Rob Clark <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: Maarten Lankhorst <[e-mail]>
Cc: Maxime Ripard <[e-mail]>
Cc: Thomas Zimmermann <[e-mail]>
Reported-by: Dmitry Baryshkov <[e-mail]>
Tested-by: Dmitry Baryshkov <[e-mail]> # test patch only
Cc: Dmitry Baryshkov <[e-mail]>
Reviewed-by: Ville Syrjälä <[e-mail]>
Reviewed-by: Rob Clark <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_atomic_helper.c

···
 	for_each_new_crtc_in_state (state, crtc, new_crtc_state, i) {
 		ktime_t v;
 
+		if (drm_atomic_crtc_needs_modeset(new_crtc_state))
+			continue;
+
+		if (!new_crtc_state->active)
+			continue;
+
 		if (drm_crtc_next_vblank_start(crtc, &v))
 			continue;