kmsaudiomixer: Remove pad if src pad could not be created

Change-Id: I1cae0b4db3aca8de487d22d64caeab0feb5be027
kmsaudiomixer: Synchronize element after linking them

Change-Id: I23aaa225f75e1707e9046faf18ce92f6e3603f99
kmsaudiomixer: show debug message if either parent or pads are NULL when requested

Change-Id: I879ed73f8bfd46d47d91add1b3812cb2d4905c28
kmsaudiomixer: Lock the state of elements before setting them to NULL_STATE

Change-Id: Ib52591c5b676e7c52282e96e395d2ef4b6ee2bc1