wifi: mac80211: fix beacon interval calculation overflow

As we are converting from TU to usecs, a beacon interval of
100*1024 usecs will lead to integer wrapping. To fix change
to use a u32.

Fixes: 057d5f4b ("mac80211: sync dtim_count to TSF")
Signed-off-by: Lachlan Hodges <lachlan.hodges@morsemicro.com>
Link: https://patch.msgid.link/20250621123209.511796-1-lachlan.hodges@morsemicro.com


Signed-off-by: Johannes Berg <johannes.berg@intel.com>