ASoC: ti: omap-mcbsp: Fix runtime PM underflow warnings

We need to check for an active device as otherwise we get warnings
for some mcbsp instances for "Runtime PM usage count underflow!".

Reported-by: Andreas Kemnade <andreas@kemnade.info>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20231030052340.13415-1-tony@atomide.com


Signed-off-by: Mark Brown <broonie@kernel.org>