pc: Fix "prog_if" typo on PC_COMPAT_2_0

The property name is "prog_if", not "prof_if".

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reported-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>