[IA64] SGI SN drivers: don't report !sn2 hardware as an error

This stuff is all in the generic ia64 kernel, and the new initcall error
reporting complains about them.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>