ASoC: wm5110: Unregister compressed platform when driver is removed

The driver was not unregistering the compressed platform in
wm5110_remove(). If the codec is built as a module, this would
lead to a NULL pointer deref if the module was unloaded and then
re-probed.

Signed-off-by: Richard Fitzgerald <rf@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>