ax25: Replace kfree() in ax25_dev_free() with ax25_dev_put()

ax25: Replace kfree() in ax25_dev_free() with ax25_dev_put()

The object "ax25_dev" is managed by reference counting. Thus it should
not be directly released by kfree(), replace with ax25_dev_put().

Fixes: d01ffb9eee4a ("ax25: add refcount in ax25_dev to avoid UAF bugs")
Suggested-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/20240530051733.11416-1-duoming@zju.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>