firmware: arm_scmi: Fix devres allocation device in virtio transport

SCMI virtio transport device managed allocations must use the main
platform device in devres operations instead of the channel devices.

Cc: Peter Hilber <peter.hilber@opensynergy.com>
Fixes: 46abe13b ("firmware: arm_scmi: Add virtio transport")
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/20221028140833.280091-5-cristian.marussi@arm.com


Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>