Fix checkpatch issue:
ERROR: do not use assignment in if condition

Replace repeated calls to device_create_file() with calls to sysfs_create_group.

Cc: Jean Delvare <khali@linux-fr.org>
Cc: Jim Cromie <jim.cromie@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>