ASoC: Use spi_write() for SPI writes

do_spi_write() is just an open coded copy of do_spi_write() so we can
delete it and just call spi_write() directly.  Indeed, as a result of
recent refactoring all the SPI write functions are just very long
wrappers around spi_write() which don't add anything except for some
pointless copies so we can just use spi_write() as the hw_write
operation directly. It should be as type safe to do this as it is to do
the same thing with I2C and it saves us a bunch of code.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@ti.com>