video/fbdev: fix defio's fsync

fb_deferred_io_fsync() returns the value of schedule_delayed_work() as
an error code, but schedule_delayed_work() does not return an error. It
returns true/false depending on whether the work was already queued.

Fix this by ignoring the return value of schedule_delayed_work().

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: stable@vger.kernel.org