hwmon: (pmbus/core) Make debugfs code unconditional

Drop contitionals around debugfs code to compile it unconditionally.
In practice it will be optimized away by the compiler if CONFIG_DEBUG_FS
is not enabled, so the code size is not affected by this change.

Also silently ignore errors if debugfs initialization fails.

Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>