wifi: iwlwifi: mvm: handle debugfs names more carefully

wifi: iwlwifi: mvm: handle debugfs names more carefully

With debugfs=off, we can get here with the dbgfs_dir being
an ERR_PTR(). Instead of checking for all this, which is
often flagged as a mistake, simply handle the names here
more carefully by printing them, then we don't need extra
checks.

Also, while checking, I noticed theoretically 'buf' is too
small, so fix that size as well.

Cc: stable@vger.kernel.org
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218422
Fixes: c36235acb34f ("wifi: iwlwifi: mvm: rework debugfs handling")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240320232419.4dc1eb3dd015.I32f308b0356ef5bcf8d188dd98ce9b210e3ab9fd@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>