hwmon: (max1619) Convert to use regmap

Use regmap for local caching, to hide register read/write address
differences, and for multi-byte operations. With this change,
the driver specific lock is no longer necessary.

While at it, check errors seen when initializing the chip and bail out
if chip initialization fails.
Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/max1619.rst

@@ -27,7 +27,3 @@ All temperature values are given in degrees Celsius. Resolution
 is 1.0 degree for the local temperature and for the remote temperature.
 
 Only the external sensor has high and low limits.
-
-The max1619 driver will not update its values more frequently than every
-other second; reading them more often will do no harm, but will return
-'old' values.