ASoC: arizona: Fix TDM slot length handling in arizona_hw_params

TDM slot length was set same as word length, regardless of the value
received in set_tdm_slot. This patch sets the TDM slot length correctly
as received in set_tdm_slot DAI callback

Signed-off-by: Nikesh Oswal <Nikesh.Oswal@wolfsonmicro.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@linaro.org>