p2m: use correct p2m_type_t in clear_mmio_p2m_entry

clear_mmio_p2m_entry() should mark the gfn as invalid.
Use proper name instead of numerical value. The currently used value of
zero means p2m_ram_rw.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Tim Deegan <tim@xen.org>
Committed-by: Tim Deegan <tim@xen.org>

xen/arch/x86/mm/p2m.c

@@ -628,7 +628,7 @@ clear_mmio_p2m_entry(struct domain *d, unsigned long gfn)
         return 0;
     }
     p2m_lock(p2m);
-    rc = set_p2m_entry(p2m, gfn, _mfn(INVALID_MFN), 0, 0, p2m->default_access);
+    rc = set_p2m_entry(p2m, gfn, _mfn(INVALID_MFN), 0, p2m_invalid, p2m->default_access);
     audit_p2m(p2m, 1);
     p2m_unlock(p2m);