w83627ehf: Fix unchecked return status

Fix: check return value from device_create_file()
Fix: call device_remove_file() on error and module unload
Fix: call hwmon_device_register() after device_create_file() to eliminate race
Signed-off-by: David Hubbard <david.c.hubbard@gmail.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>