memory: samsung: exynos5422-dmc: rename timing register fields variables

The driver has file-scope arrays defining fields of timing registers
(e.g. struct timing_reg timing_row) and actual values for these
registers per each OPP in state container (struct
exynos5_dmc.timing_row).  The meanings of these are different so use
different names to avoid confusion.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://lore.kernel.org/r/20200822163218.21857-1-krzk@kernel.org