Commit 97fd1ea8 broke the build for --without-default-devices as
VMMOUSE depends on VMPORT.

Fixes: 97fd1ea8
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>