drm/crc: Only open CRC on atomic drivers when the CRTC is active.

Commit e8fa5671 ("drm: crc: Wait for a frame before returning
from open()") adds a wait for CRC frame, but with the CRTC off
this will never be generated. For atomic drivers we know if a CRTC
is active through crtc_state->active, so when inactive reject the
open with -EIO.

Just like with the previous patch changing debugfs opening semantics,
this patch has been tested against igt.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Fixes: e8fa5671 ("drm: crc: Wait for a frame before returning from open()")
Testcase: debugfs_test.read_all_entries
Link: http://patchwork.freedesktop.org/patch/msgid/15f9d300-65d3-63aa-00e3-e83f5e4d5a7a@linux.intel.com


Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>