Simplify function logic by using g_autofree to free local variables so
that we can remove some goto statements that are used for cleanup.

Introduce a g_autoptr cleanup function for virNodeDeviceDef.
Signed-off-by: NJonathon Jongsma <jjongsma@redhat.com>
Reviewed-by: NErik Skultety <eskultet@redhat.com>