ASoC: samsung: Add missing prepare for iis clock of s3c24xx

The s3c_i2sv2_probe() only enabled iis clock.  Missing prepare isn't
probably fatal, because for SoC clocks this is usually no-op, but for
correctness this clock should be prepared.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Arvind <Yadav&lt;arvind.yadav.cs@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>