Bluetooth: Fix possible access of hci_chan after it is deleted

When the connection is not in BT_CONNECTED state it was possible
for code in hci_chan_modify() to attempt to access the hci_chan
structure after it had already been deleted by hci_chan_put().

Change-Id: I5ae352ac12aa3b456e7bcf30633015d98b03e44b
CRs-fixed: 319934
Signed-off-by: Peter Krystad <pkrystad@codeaurora.org>