wifi: ath6kl: reduce WARN to dev_dbg() in callback

wifi: ath6kl: reduce WARN to dev_dbg() in callback

[ Upstream commit 75c4a8154cb6c7239fb55d5550f481f6765fb83c ]

The warn is triggered on a known race condition, documented in the code above
the test, that is correctly handled.  Using WARN() hinders automated testing.
Reducing severity.

Fixes: b36fa1192f6c ("ath6kl: Fix kernel panic on continuous driver load/unload")
Reported-and-tested-by: syzbot+555908813b2ea35dae9a@syzkaller.appspotmail.com
Signed-off-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230126182431.867984-1-pchelkin@ispras.ru
Signed-off-by: Sasha Levin <sashal@kernel.org>