ASoC: wm5110: Fix up snd_soc_register_platform error path

Whilst there is nothing wrong with the error path here it looks a little
bit odd, this patches makes the code a little more idiomatic.

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