ASoC: tpa6130a2: Simplify power state management

Use simpler way to avoid setting the same power state
for the amplifier.
Simplifies the check introduced by patch:
ASoC: tpa6130a2: Fix unbalanced regulator disables

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Cc: Jarkko Nikula <jhnikula@gmail.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>