drm/omap: remove extra plane->destroy from crtc destroy

All the planes, including primary planes, are now destroyed by the drm
framework. Thus we no longer need the explicit call to plane->destroy
from the crtc's destroy function.

This patch removes the call, thus fixing the crash caused by double
freeing the plane.

remove omap_crtc->plane->funcs->destroy(omap_crtc->plane)

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