scripts/modpost: check for bad references in .pci.fixups area

Functions used for PCI fixups (like DECLARE_PCI_FIXUP_HEADER) are often
marked __init. This is okay as long as nobody is using PCI hotplug.
However if one does execute
| echo 1 > /sys/bus/pci/rescan

and we hit a module which is marked __init istead of __devinit then we
go boom because the code is removed after the kernel booted. This patch
help to see those section mismatches.

Cc: Michal Marek <mmarek@suse.cz>
Cc: linux-kbuild@vger.kernel.org
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>