PCI/AER: Factor message prefixes with dev_fmt()

Define dev_fmt() with the common prefix of log messages so we don't have to
repeat it in every printk.  No functional change intended.

Link: https://lore.kernel.org/r/20191213225709.GA213811@google.com


Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>