hwmon: (pmbus) Expand scope of device specific get_status function

Some devices use non-standard registers to access various functionality.
This does not only affect status registers, but other registers as well.
Rename local get_status function to get_byte_data to reflect this requirement.

Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
Reviewed-by: Tom Grennan <tom.grennan@ericsson.com>