Commit 57b8ff07 ("driver core: add devm_device_add_group() and
friends") has added the managed version for creating sysfs group files.

Use devm_device_add_group instead of sysfs_create_group and remove the
action that cleans the sysfs file when exiting the driver.
Signed-off-by: NAndi Shyti <andi@etezian.org>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>