drm/i915: move i915_get_extra_insdone out of CONFIG_DEBUG_FS block

Otherwise it just won't compile ...

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@gmail.com>