mtd: s3c2410: Fix compiler warnings

mtd: s3c2410: Fix compiler warnings

Fixes the following warnings:
‘s3c2410_nand_correct_data’ defined but not used [-Wunused-function]
‘s3c2410_nand_enable_hwecc’ defined but not used [-Wunused-function]
‘s3c2412_nand_enable_hwecc’ defined but not used [-Wunused-function]
‘s3c2440_nand_enable_hwecc’ defined but not used [-Wunused-function]
‘s3c2410_nand_calculate_ecc’ defined but not used [-Wunused-function]
‘s3c2412_nand_calculate_ecc’ defined but not used [-Wunused-function]
‘s3c2440_nand_calculate_ecc’ defined but not used [-Wunused-function]

The above functions are called only when CONFIG_MTD_NAND_S3C2410_HWECC
is defined. Thus making them conditional.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>