firmware: arm_ffa: Add pointer to the ffa_dev_ops in struct ffa_dev

firmware: arm_ffa: Add pointer to the ffa_dev_ops in struct ffa_dev

Currently ffa_dev_ops_get() is the way to fetch the ffa_dev_ops pointer.
It checks if the ffa_dev structure pointer is valid before returning the
ffa_dev_ops pointer.

Instead, the pointer can be made part of the ffa_dev structure and since
the core driver is incharge of creating ffa_device for each identified
partition, there is no need to check for the validity explicitly if the
pointer is embedded in the structure.

Add the pointer to the ffa_dev_ops in the ffa_dev structure itself and
initialise the same as part of creation of the device.

Link: https://lore.kernel.org/r/20220907145240.1683088-2-sudeep.holla@arm.com
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>