We don't have any caller passing a NULL device argument,
so we can simplify, avoiding to access the global 'isabus'.

(Since the previous commit, isa_address_space_io() assert
 the device argument is not NULL).

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 hw/isa/isa-bus.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/isa/isa-bus.c b/hw/isa/isa-bus.c
index 08c84704e9..abc1bd0771 100644
--- a/hw/isa/isa-bus.c
+++ b/hw/isa/isa-bus.c
@@ -120,7 +120,7 @@ static inline void isa_init_ioport(ISADevice *dev, uint16_t ioport)
 
 void isa_register_ioport(ISADevice *dev, MemoryRegion *io, uint16_t start)
 {
-    memory_region_add_subregion(isabus->address_space_io, start, io);
+    memory_region_add_subregion(isa_address_space_io(dev), start, io);
     isa_init_ioport(dev, start);
 }
 
-- 
2.38.1