2.6.36-rc2 build failure: implicit declaration of function 'seq_printf'

[Sven Joachim]

Commit 6ef3d4278034982c13df87c4a51e0445f762d316 causes a build failure
for me:

,----
|   CC [M]  drivers/gpu/drm/i915/intel_overlay.o
| 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'
| make[4]: *** [drivers/gpu/drm/i915/intel_overlay.o] Error 1
`----

Adding a line with

#include <linux/seq_file.h>

to intel_overlay.c fixes this.  Looking at include/drm/*.h, I notice
that <linux/seq_file.h> is only #included if CONFIG_DEBUG_FS is set,
which is not the case in my configuration.

Sven