Function pci_bridge_emul_init() may fail so correctly check for errors.

Link: https://lore.kernel.org/r/20200907111038.5811-3-pali@kernel.org
Fixes: 8a3ebd8d ("PCI: aardvark: Implement emulated root PCI bridge config space")
Signed-off-by: NPali Rohár <pali@kernel.org>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: NMarek Behún <marek.behun@nic.cz>