ARM: samsung: Omit superfluous error message in s3c_adc_probe()

In the function s3c_adc_probe(), when get irq failed, the function
platform_get_irq() logs an error message, so remove redundant
message here.

Signed-off-by: Shengju Zhang <zhangshengju@cmss.chinamobile.com>
Signed-off-by: Tang Bin <tangbin@cmss.chinamobile.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>