ia64/traps: Silence GCC warning about uninitialised variable

  arch/ia64/kernel/traps.c: In function 'ia64_fault':
  arch/ia64/kernel/traps.c:433:17: warning: 'siginfo.si_code' may be used uninitialized in this function [-Wmaybe-uninitialized]
    struct siginfo siginfo;

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>