drm: plug memory leak on drm_setup() failure

Currently we fail to free and detach the drm_file when drm_setup() fails.
Use the drm_close_helper to do address that.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114084410.15266-2-emil.l.velikov@gmail.com