st/va: do not destroy old buffer when new one failed

st/va: do not destroy old buffer when new one failed

If formats are not the same vlVaPutImage re-creates the video
buffer with the right format. But if the creation of this new
video buffer fails then the surface looses its current buffer.
Let's just destroy the previous buffer on success.

Signed-off-by: Julien Isorce <j.isorce@samsung.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Christian König <christian.koenig@amd.com>