ASoC: sglt5000: Provide the reg_stride field

sgtl5000 has 16-bit registers, and only even numbers are valid for its registers
addresses.

Let regmap knows about this feature by specifying the 'reg_stride' field, so
that it can access only the valid registers.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Mark Brown <broonie@linaro.org>