PCI: keystone: Remove unnecessary goto statement

Fix the misuse of goto statement in ks_pcie_get_irq_controller_info() as
simple return is more appropriate for this function.  While at it add an
error log for absence of interrupt controller node.

[bhelgaas: drop "ret" altogether since we always know the return value]
Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: Rob Herring <robh+dt@kernel.org>
CC: Pawel Moll <pawel.moll@arm.com>
CC: Mark Rutland <mark.rutland@arm.com>
CC: Ian Campbell <ijc+devicetree@hellion.org.uk>
CC: Kumar Gala <galak@codeaurora.org>