Input: s3c2410_ts: fix S3C_ADC dependency

S3C_ADC is only available on machines that don't do ARCH_MULTIPLATFORM,
so changing the 'select' into 'depends on' here helps us move to
ARCH_MULTIPLATFORM without introducing regressions.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>