mac80211: fix ht_capa printout in debugfs

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

Fixes: 01f84f0ed3b4 ("mac80211: reduce stack usage in debugfs")
Signed-off-by: Ben Greear <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
[correct the Fixes tag]
Signed-off-by: Johannes Berg <[e-mail]>

net/mac80211/debugfs_sta.c

···
 #define PRINT_HT_CAP(_cond, _str) \
 	do { \
 	if (_cond) \
-			p += scnprintf(p, sizeof(buf)+buf-p, "\t" _str "\n"); \
+			p += scnprintf(p, bufsz + buf - p, "\t" _str "\n"); \
 	} while (0)
 	char *buf, *p;
 	int i;