ASoC: AD1836: drop unnecessary spi register check

The only thing the init func does is register a spi driver, so if that
fails, we return the value back up to the caller who will display an
error message for us.  So drop the redundant checking/message.

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