powerpc/pci: Remove legacy debug code

Commit 59f47eff ("powerpc/pci: Use of_irq_parse_and_map_pci() helper")
removed the 'oirq' variable, but kept memsetting it when the DEBUG macro is
defined.

When setting DEBUG macro for debugging purpose, the kernel fails to build since
'oirq' is not defined anymore.

This patch simply remove the debug block, since it does not seem to sense
now.

Fixes: 59f47eff ("powerpc/pci: Use of_irq_parse_and_map_pci() helper")

Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>