arm: exynos: Use proper ADC device name

Since commit 4213609c ("drivers: core: use strcmp when find device by
name") one has to provide full name to get requested object. Fix the code
used to detect Odroid board revision to use proper ADC device name then.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Anand Moon <linux.amoon@gmail.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>