mptcp: pm: remove unused ret value to set flags

The returned value is not used, it can then be dropped.

Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20250221-net-next-mptcp-pm-misc-cleanup-3-v1-1-2b70ab1cee79@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>