If it is necessary to re-initialize the chip, for example because
it has been power cycled, use regmap functions to update register
contents. This ensures that all registers, including the configuration
register and alert registers, are updated to previously configured
values without having to locally cache everything.

For this to work, volatile registers have to be marked as volatile.
Also, the cache needs to be bypassed when reading the calibration
and mask_enable registers. While the calibration register is not
volatile, it will be reset to 0 if the chip has been power cycled.
Most of the bits in the mask_enable register are configuration bits,
except for bit 4 which reports if an alert has been observed.
Both registers need to be marked as non-volatile to be updated
after a power cycle, but it is necessary to bypass the cache when
reading them to detect if the chip has been power cycled and to
read the alert status.

The chip does not support register auto-increments. It is therefore
necessary to configure regmap to use single register read/write
operations. Otherwise regmap tries to write all registers in a single
operation when synchronizing register contents with the hardware,
and the synchronization fails.

Another necessary change is to declare ina226_alert_to_reg() as u16.
So far it returned an s16 which is sign extended to a large negative
value which is then sent to regmap as unsigned int, causing an -EINVAL
error return.
Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>