drm/omap: Remove unnecessary display output sanity checks

The omapdrm driver checks at suspend and resume time whether the
displays it operates on have their driver operations set. This check is
unneeded, as all display drivers set the driver operations field at
probe time and never touch it afterwards. This is furthermore proven by
the dereferencing of the driver field without checking it first in
several locations.

The omapdss driver performs a similar check at shutdown time. This is
unneeded as well, as the for_each_dss_display() macro it uses to iterate
over displays locates the displays by checking the driver field
internally.

As those checks are unnecessary, remove them.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>