plugins: Avoid re-create new vaapi memory allocator in set_config()
gst_vaapi_video_buffer_pool_set_config will re-create a new vaapi memory allocator when the allocator param is not correct. The new re-create vaapi memory allocator use default allocation param and the behavior is different from what we want. Just re-use the valid allocator rather than re-create a new one when the allocator param is not valid.
Signed-off-by: He Junyan junyan.he@hotmail.com
Edited by He Junyan