ASoC: wm5100: Export wm5100_detect

Export the symbol so that it is accessible to modules. Fixes the
following error:

ERROR: "wm5100_detect" [sound/soc/samsung/snd-soc-lowland.ko] undefined!

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@linaro.org>