powerpc/eeh: Cleanup eeh_gather_pci_data()

The patch replaces printk(KERN_WARNING ...) with pr_warn() in the
function eeh_gather_pci_data().

Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>