ASoC: da7219: Disallow unsupported 32KHz clock setting in set_dai_sysclk()

The PLL function was updated to disallow 32KHz in
commit 501f72e9 ("ASoC: da7219: Remove support for 32KHz PLL mode"),
but set_dai_sysclk() was missed and still permits it. This patch resolves
that discrepancy.

Signed-off-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
Signed-off-by: Mark Brown <broonie@kernel.org>