ASoC: davinci-mcasp: Correct pm status check in suspend callback

pm_runtime_enabled() will only tell if the pm runtime has been enabled for
the device, which is done at probe time but will not tell the actual power
state of the device.
pm_runtime_active() provides this information.
This patch fixes a kernel crash when doing suspend when McASP is not
active.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>