staging: vc04_services: vchiq_mmal: Rename service_callback()

Rename the service_callback static function to mmal_service_callback()
since the function signature conflicts with:

extern int
service_callback(struct vchiq_instance *vchiq_instance, enum vchiq_reason reason,
                 struct vchiq_header *header, unsigned int handle, void *bulk_userdata);

in vc04_services/interface/vchiq_arm/vchiq_arm.h

In a subsequent patch, we will include vchiq_arm.h header to
mmal-vchiq.c, which will then complain of this conflict. Hence,
this patch is meant to handle the conflict beforehand.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Stefan Wahren <wahrenst@gmx.net>
Link: https://lore.kernel.org/r/20240412075743.60712-10-umang.jain@ideasonboard.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>