q35: Use PC_Q35_COMPAT_1_4 on pc-q35-1.4 compat_props

pc-q35-1.4 was incorrectly using PC_COMPAT_1_4 instead of
PC_Q35_COMPAT_1_4.

The only side-effect was that the hpet compat property (inherited from
PC_Q35_COMPAT_1_7) was missing.

Without this patch, pc-q35-1.4 inicorrectly initializes hpet-intcap to
0xff0104 (behavior introduced in QEMU 2.0, by commit
7a10ef51c2397ac4323bc786af02c58b413b5cd2).

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Reviewed-by: Markus Armbruster <armbru@redhat.com>
