PCI: static local variable

[Maxime Villard <max%m00nbsd.net@localhost>]

I noticed in xpci_xenbus.c::pci_conf_read that a variable is defined as
static, and I suspect this is a typo.

pci_conf_read is called from many drivers, which can be MP-safe, and
could concurrently call the function, resulting in corrupted return values
on domUs (where SMP is enabled).

Can someone proof-read? If that's indeed a bug we'll have to pull up the
fix to NetBSD 7/8.

Thanks,
Maxime