hwmon: (f75375s) Fix warning message seen in some configurations
In some configurations, BUG() does not result in an endless loop but returns to
the caller. This results in the following compiler warning:
drivers/hwmon/f75375s.c: In function 'duty_mode_enabled':
drivers/hwmon/f75375s.c:280: warning: control reaches end of non-void function
drivers/hwmon/f75375s.c: In function 'auto_mode_enabled':
drivers/hwmon/f75375s.c:295: warning: control reaches end of non-void function
Fix the warning by returning something sensible after BUG().