ia64/PCI: Fix incorrect PCI resource end address

commit f976721e ("ia64/PCI: Use ioremap() instead of open-coded
equivalent") introduced the following compiler warning,

  arch/ia64/sn/kernel/io_init.c: In function 'sn_io_slot_fixup':
  arch/ia64/sn/kernel/io_init.c:189:19: warning: 'addr' may be used uninitialized in this function [-Wmaybe-uninitialized]
     res->end = addr + size;
                   ^

'addr' is indeed uninitialised and the correct value to use is
res->start.

Cc: Tony Luck <tony.luck@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Bjorn Helgaas <helgaas@kernel.org>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Tony Luck <tony.luck@intel.com>