drm/nouveau/kms/nv50-: Call outp_atomic_check_view() before handling PBN

commit 310d3577

 upstream.

Since nv50_outp_atomic_check_view() can set crtc_state->mode_changed, we
probably should be calling it before handling any PBN changes. Just a
precaution.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Fixes: 232c9eec

 ("drm/nouveau: Use atomic VCPI helpers for MST")
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Juston Li <juston.li@intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: <stable@vger.kernel.org> # v5.1+
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>