patman: Fix defaults not propagating to subparsers

On python 3.8.10 (and 3.10), subparsers are not updated with defaults. I
suspect this is related to [1]. Fix this by explicitly updating
subparsers with settings.

[1] https://github.com/python/cpython/issues/89398



Fixes: 3145b635 ("patman: Update defaults in subparsers")
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Tested-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>