qxl: check qxl_phys2virt return value

Fixes: CID 1395986
Fixes: 979f7ef8966bc4495a710ed9e4af42098f92ee79
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20181005134608.1251-1-kraxel@redhat.com
1 file changed