ASoC: wm8978: Adjust clock indices so that simple card works

Using simple-card with the wm8978 doesn't work because simple card calls
set_sysclk on the clock index 0, which is not the MCLK in the WM8978.

Adjust the clock definition so that the clock 0 is the MCLK.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Mark Brown <broonie@kernel.org>