vga: update vga register setup on vbe changes

Call the new vbe_update_vgaregs() function on vbe configuration
changes, to make sure vga registers are up-to-date.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/display/vga.c

@@ -763,6 +763,7 @@ void vbe_ioport_write_data(void *opaque, uint32_t addr, uint32_t val)
         case VBE_DISPI_INDEX_Y_OFFSET:
             s->vbe_regs[s->vbe_index] = val;
             vbe_fixup_regs(s);
+            vbe_update_vgaregs(s);
             break;
         case VBE_DISPI_INDEX_BANK:
             val &= s->vbe_bank_mask;