OMAP: OMAPFB: add dummy release function for omapdss

This should fix:
WARNING: at drivers/base/core.c:131 device_release+0x68/0x7c()
Device 'omapdss' does not have a release() function, it is broken and
must be fixed.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>