mac80211: fix ht_capa printout in debugfs

Don't use sizeof(pointer) when calculating scnprintf offset.

Fixes: 01f84f0e ("mac80211: reduce stack usage in debugfs")
Signed-off-by: Ben Greear <greearb@candelatech.com>
Link: https://lore.kernel.org/r/20220406175659.20611-1-greearb@candelatech.com


[correct the Fixes tag]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>