media: staging/ipu7: cleanup the MMU correctly in IPU7 driver release

IPU7 ISYS and PSYS auxiliary devices are released after
ipu7_bus_del_devices(), so driver can not reference the MMU devices
from ISYS and PSYS auxiliary devices, so move the MMUs cleanup before
releasing the auxiliary devices.

Fixes: b7fe4c00 ("media: staging/ipu7: add Intel IPU7 PCI device driver")
Signed-off-by: Bingbu Cao <bingbu.cao@intel.com>
[Sakari Ailus: Drop extra newline.]
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>