cirrus: Unbreak ISA support

Do not try to map against the PCI bar in the ISA version of the device.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/cirrus_vga.c

@@ -2401,7 +2401,7 @@ static void map_linear_vram_bank(CirrusVGAState *s, unsigned bank)
 
 static void map_linear_vram(CirrusVGAState *s)
 {
-    if (!s->linear_vram) {
+    if (s->bustype == CIRRUS_BUSTYPE_PCI && !s->linear_vram) {
         s->linear_vram = true;
         memory_region_add_subregion_overlap(&s->pci_bar, 0, &s->vga.vram, 1);
     }
@@ -2411,7 +2411,7 @@ static void map_linear_vram(CirrusVGAState *s)
 
 static void unmap_linear_vram(CirrusVGAState *s)
 {
-    if (s->linear_vram) {
+    if (s->bustype == CIRRUS_BUSTYPE_PCI && s->linear_vram) {
         s->linear_vram = false;
         memory_region_del_subregion(&s->pci_bar, &s->vga.vram);
     }