ASoC: mpc5200_psc_ac97: Remove unused on-stack snd_ac97 device

The mpc5200_psc_ac97 driver puts a snd_ac97 device on the stack in the
driver probe function, initializes the private data member of the device and
the never uses the device again. It should be safe to remove it.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>