drivers/gpu/drm/i915/intel_overlay.c needs seq_file.h

drivers/gpu/drm/i915/intel_overlay.c needs seq_file.h

drivers/gpu/drm/i915/intel_overlay.c: In function 'intel_overlay_print_error_state':

drivers/gpu/drm/i915/intel_overlay.c:1467: error: implicit declaration of function 'seq_printf'

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=16811

Reported-by: Martin Ziegler <ziegler@uni-freiburg.de>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Eric Anholt <eric@anholt.net>
Cc: Dave Airlie <airlied@linux.ie>
Cc: Andre Muller <andremuellerster@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>