[media] omap3isp: stat: Remove impossible WARN_ON

The WARN_ON statements in the buffer allocation functions try to catch
conditions where buffers would have already been allocated. As the
buffers are explicitly freed right before being allocated this can't
happen.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>