Bluetooth: Remove unnecessary check for chan->psm

Now that ATT sockets have been converted to use the new L2CAP_CHAN_FIXED
type there is no need to have an extra check for chan->psm in the
l2cap_chan_close function.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>