drm/hdlcd: Don't call drm_crtc_vblank_off on unbind

This is already taken care of by drm_atomic_helper_shutdown(), and
in that case only for the CRTC which are actually on.

Only tricky bit here is that we kill the interrupt handling before we
shut down crtc, so need to reorder that.

Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Brian Starkey <brian.starkey@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200602095140.36678-3-daniel.vetter@ffwll.ch