memory: samsung: exynos5422-dmc: Fix kfree() of devm-allocated memory and missing static

Fix issues captured by static checkers: use of kfree() on
resource-managed memory and missing 'static' in the private function.

Fixes Smatch warning:
    drivers/memory/samsung/exynos5422-dmc.c:272
        exynos5_init_freq_table() warn: passing devm_ allocated variable to kfree. 'dmc->opp'

Fixes Sparse warning:
    drivers/memory/samsung/exynos5422-dmc.c:736:1:
        warning: symbol 'exynos5_dmc_align_init_freq' was not declared.

Reported-by: kbuild test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Reported-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Lukasz Luba <l.luba@partner.samsung.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>