ASoC: wm8731: Adjust clk definitions so that simple card can work

ASoC: wm8731: Adjust clk definitions so that simple card can work

When trying to use simple card with wm8962 the following probe
error happens:

  wm8731 0-001a: simple-card: set_sysclk error

In simple-card.c the snd_soc_dai_set_sysclk() function is called with
clk_id as 0, which is an invalid clock for wm8731.

Adjust the clocks source definitions in wm8731.h so that the simple
card driver can work successfully

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Mark Brown <broonie@kernel.org>