In 01ccb69, changes to the MB CPLD code were made which caused the
following issue when updating the CPLD:
root@ni-x4xx-xxxxxxx:~# zbx_update_cpld --dboards 0
Traceback (most recent call last):
File "/usr/bin/zbx_update_cpld", line 22, in <module>
from usrp_mpm.periph_manager.x4xx_mb_cpld import MboardCPLD
ImportError: cannot import name 'MboardCPLD' from
'usrp_mpm.periph_manager.x4xx_mb_cpld'
(/usr/lib/python3.7/site-packages/usrp_mpm/periph_manager/x4xx_mb_cpld.py)
This fixes this bug.