firmware: arm_ffa: Simplify probe function

When the driver core calls the probe callback it already checked that
the devices match, so there is no need to call the match callback again.

Link: https://lore.kernel.org/r/20210621201652.127611-2-u.kleine-koenig@pengutronix.de


Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>