memory: samsung: exynos5422-dmc: Additional locking for 'curr_rate'

memory: samsung: exynos5422-dmc: Additional locking for 'curr_rate'

The 'curr_rate' is protected by local 'dmc->lock' in various places, but
not in a function exynos5_dmc_get_status(). The lock protects frequency
(and voltage) change process and the corresponding value stored in
'curr_rate'. Add the locking mechanism to protect the 'curr_rate' reading
also in the exynos5_dmc_get_status().

Suggested-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://lore.kernel.org/r/20200811101727.3976-1-lukasz.luba@arm.com
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>