spapr_pci: drop useless check in spapr_phb_vfio_get_loc_code()

g_strdup_printf() either returns a non-null pointer, or aborts if it
failed to allocate memory.

Signed-off-by: Greg Kurz <groug@kaod.org>
[dwg: Grammatical fix to commit message]
Acked-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
