spapr_pci: fix potential NULL pointer dereference

spapr_pci: fix potential NULL pointer dereference

Commit 2c88b098e76fd added a call to SPAPR_MACHINE_GET_CLASS(spapr) in
spapr_phb_realize() before we check spapr isn't NULL. This causes QEMU
to crash when starting a non-pseries machine with a sPAPR PHB.

This could be fixed by setting the smc variable after the null check,
but it seems more explicit to use a ternary operator to skip the call
to SPAPR_MACHINE_GET_CLASS() if spapr is NULL, since spapr_phb_realize()
will return immediately in this case.

This was reported by Coverity (CID 1395170 and 1395183).

Fixes: 2c88b098e76fde0c7fcc0476dd3f80ce58409505
Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>