drm/doc: Fix copy paste error in drm_crtc_funcs.destroy()

The function is about cleaning up CRTC resources, not plane resources,
fix this in docbook.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
1 file changed