msdk: ignore MFX_ERR_UNDEFINED_BEHAVIOR when loading a plugin

msdk: ignore MFX_ERR_UNDEFINED_BEHAVIOR when loading a plugin

An issue can be seen when using msdkh265enc with bitrate change in
playing state. The root cause is the corresponding plugin is loaded
again.

Returning MFX_ERR_UNDEFINED_BEHAVIOR from MSDK just means the plugin has
been loaded, so we may ignore this error when doing configuation again
in the sub class, otherwise the pipeline will be interrupted