rtc: max77686: Use single-byte writes on MAX77620

The MAX77620 doesn't support bulk writes, so make sure the regmap code
breaks bulk writes into multiple single-byte writes.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Link: https://lore.kernel.org/r/20200417170825.2551367-3-thierry.reding@gmail.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>