drm: Fix kernel docs for drm_helper_mode_fill_fb_struct()

drm: Fix kernel docs for drm_helper_mode_fill_fb_struct()

drm_modeset_helper.c:74: warning: No description found for parameter 'dev'

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Fixes: ae2f5cc033d3 ("drm: Pass 'dev' to drm_helper_mode_fill_fb_struct()")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161215170128.23972-1-ville.syrjala@linux.intel.com
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>