[ci] Add flash_ctrl_gen.py to the check-generated CI check
[ci] Add flash_ctrl_gen.py to the check-generated CI check

This check started failing with 7858f3d a week ago and we hadn't
noticed (fixed in the commit before this one).

Signed-off-by: Rupert Swarbrick <290093e2ad2515ed2f14d749293c8cf8e02ca274@lowrisc.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan