serial: samsung: Replace rd_regb/wr_regb with rd_reg/wr_reg

This patch change the name of macro for general usage.

Signed-off-by: Hyunki Koo <hyunki00.koo@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Tested on Odroid HC1 (Exynos5422):
Tested-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200506080242.18623-1-hyunki00.koo@samsung.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>