drm: fix sparse warnings on undeclared symbols in crc debugfs

drm: fix sparse warnings on undeclared symbols in crc debugfs

Fixes sparse warnings:

drivers/gpu/drm/drm_debugfs_crc.c:118:30: warning: symbol
'drm_crtc_crc_control_fops' was not declared. Should it be static?

drivers/gpu/drm/drm_debugfs_crc.c:264:30: warning: symbol
'drm_crtc_crc_data_fops' was not declared. Should it be static?

drivers/gpu/drm/drm_debugfs_crc.c:281:5: warning: symbol
'drm_debugfs_crtc_crc_add' was not declared. Should it be static?

Fixes: 9edbf1fa600a ("drm: Add API for capturing frame CRCs")
Cc: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Emil Velikov <emil.velikov@collabora.com>
Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1476790115-28665-1-git-send-email-jani.nikula@intel.com