Bluetooth: hci_qca: fix debugfs registration

Bluetooth: hci_qca: fix debugfs registration

commit 47c5d829a3e326b7395352a10fc8a6effe7afa15 upstream.

Since commit 3e4be65eb82c ("Bluetooth: hci_qca: Add poweroff support
during hci down for wcn3990"), the setup callback which registers the
debugfs interface can be called multiple times.

This specifically leads to the following error when powering on the
controller:

	debugfs: Directory 'ibs' with parent 'hci0' already present!

Add a driver flag to avoid trying to register the debugfs interface more
than once.

Fixes: 3e4be65eb82c ("Bluetooth: hci_qca: Add poweroff support during hci down for wcn3990")
Cc: stable@vger.kernel.org	# 4.20
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>