sh: Fix up async PCIe probing on SMP.

For the SMP case we run in to a lockup without a full synchronization
prior to continuing with the boot.

Signed-off-by: Paul Mundt <[e-mail]>

arch/sh/drivers/pci/pcie-sh7786.c

···
 		async_schedule(sh7786_pcie_hwops->port_init_hw, port);
 	}
 
+	async_synchronize_full();
+
 	return 0;
 }
 arch_initcall(sh7786_pcie_init);