firmware: arm_ffa: Remove ffa_dev_ops_get()

firmware: arm_ffa: Remove ffa_dev_ops_get()

The only user of this exported ffa_dev_ops_get() was OPTEE driver which
now uses ffa_dev->ops directly, there are no other users for this.

Also, since any ffa driver can use ffa_dev->ops directly, there will be
no need for ffa_dev_ops_get(), so just remove ffa_dev_ops_get().

Link: https://lore.kernel.org/r/20220907145240.1683088-4-sudeep.holla@arm.com
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>