hwmon: (pmbus): Access word data for STATUS_WORD

Pmbus always reads byte data from the status register, even if
configured to use STATUS_WORD. Use a function pointer to read the
correct amount of data from the registers.
Also switch to try STATUS_WORD first before STATUS_BYTE on init.

Signed-off-by: Edward A. James <eajames@us.ibm.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>