ASoC: Clarify naming for SMDK WM9713 driver

At least some of the systems using this device have multiple audio
subsystems so provide some guidance to userspace about which one this
is.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Jassi Brar <jassi.brar@samsung.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>