PCI/AER: Log correctable errors as warning, not error

PCIe correctable errors are recovered by hardware with no need for software
intervention (PCIe r5.0, sec 6.2.2.1).

Reduce the log level of correctable errors from KERN_ERR to KERN_WARNING.

The bug reports below are for correctable error logging.  This doesn't fix
the cause of those reports, but it may make the messages less alarming.

[bhelgaas: commit log, use pci_printk() to avoid code duplication]
Link: https://bugzilla.kernel.org/show_bug.cgi?id=201517
Link: https://bugzilla.kernel.org/show_bug.cgi?id=196183
Link: https://lore.kernel.org/r/20200618155511.16009-1-Kangie@footclan.ninja


Signed-off-by: Matt Jolly <Kangie@footclan.ninja>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>