omapfb: Return error code when applying overlay settings fails

the check of the return code is missing, user space does not get notified
about the error condition:

omapdss OVERLAY error: overlay 2 horizontally not inside the display area (403 + 800 >= 800)
omapdss APPLY error: failed to apply settings: illegal configuration.

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>