firmware: arm_scmi: optee: Make use of module_tee_client_driver()

firmware: arm_scmi: optee: Make use of module_tee_client_driver()

Reduce boilerplate by using the newly introduced module_tee_client_driver().
That takes care of assigning the driver's bus, so the explicit assigning
in this driver can be dropped.

Reviewed-by: Sumit Garg <sumit.garg@oss.qualcomm.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>