edac: i5400 fix missing CONFIG_PCI define

When building without CONFIG_PCI the edac_pci_idx variable is unused,
causing a build-time warning.  Wrap the variable in #ifdef CONFIG_PCI,
just like the rest of the PCI support.

Signed-off-by: Ira W. Snyder <iws@ovro.caltech.edu>
Signed-off-by: Doug Thompson <dougthompson@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>