staging: drm/omap: remove reclaim_buffers callback

The reclaim_buffers callback has already been removed by Daniel Vetter
<daniel.vetter@ffwll.ch> with his patch "drm: kill reclaim_buffers callback"
(b0071efe). As a result the kernel compilation fails with omapdrm support
and so the callback for reclaim_buffers is being removed from omapdrm.

Signed-off-by: Chandrabhanu Mahapatra <cmahapatra@ti.com>
Reviewed-by: Sumit Semwal <sumit.semwal@ti.com>
Signed-off-by: Rob Clark <rob@ti.com>
Acked-by: Paul Menzel <paulepanter@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>