tee: avoid explicit sysfs_create/delete_group by initialising dev->groups

If the dev->groups is initialised, the sysfs group is created as part
of device_add call. There is no need to call sysfs_create/delete_group
explicitly.

Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>