ASoC: wm8741: Set OSR mode in hw_params()

For correct operation of the digital filtering and other processing on the
WM8741, the user must ensure the correct value of OSR[1:0] is set at all
times.[1] Hence, depending the selected sampling rate, set the OSR (over-
sampling rate) mode in hw_params().

References:
	[1] "WM8741 Data Sheet"

Signed-off-by: Sergej Sawazki <sergej@taudac.com>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>