Bluetooth: Allow suspend even when preparation has failed

It is preferable to allow suspend even when Bluetooth has problems
preparing for sleep. When Bluetooth fails to finish preparing for
suspend, log the error and allow the suspend notifier to continue
instead.

To also make it clearer why suspend failed, change bt_dev_dbg to
bt_dev_err when handling the suspend timeout.

Fixes: dd522a74

 ("Bluetooth: Handle LE devices during suspend")
Reported-by: Len Brown <len.brown@intel.com>
Signed-off-by: Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>