memory: samsung: exynos5422-dmc: Avoid some over memory allocation

memory: samsung: exynos5422-dmc: Avoid some over memory allocation

'dmc->counter' is a 'struct devfreq_event_dev **', so there is some
over memory allocation. 'counters_size' should be computed with
'sizeof(struct devfreq_event_dev *)'.

Use 'sizeof(*dmc->counter)' instead to fix it.

While at it, use devm_kcalloc() instead of devm_kzalloc()+open coded
multiplication.

Fixes: 6e7674c3c6df ("memory: Add DMC driver for Exynos5422")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/69d7e69346986e2fdb994d4382954c932f9f0993.1647760213.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>