drm/armada: Remove NULL open/pre/postclose hooks

The compiler will do this, but the void hits when grepping all the
hooks for a subsystem wide audit are slightly annoying. So remove them
for next time around.

Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1452548477-15905-8-git-send-email-daniel.vetter@ffwll.ch
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

drivers/gpu/drm/armada/armada_drv.c

@@ -188,9 +188,6 @@ static const struct file_operations armada_drm_fops = {
 
 static struct drm_driver armada_drm_driver = {
 	.load			= armada_drm_load,
-	.open			= NULL,
-	.preclose		= NULL,
-	.postclose		= NULL,
 	.lastclose		= armada_drm_lastclose,
 	.unload			= armada_drm_unload,
 	.set_busid		= drm_platform_set_busid,