Bluetooth: MGMT: Add error handling to pair_device()

commit 538fd3921afac97158d4177139a0ad39f056dbb2 upstream.

hci_conn_params_add() never checks for a NULL value and could lead to a NULL
pointer dereference causing a crash.

Fixed by adding error handling in the function.

Cc: Stable <stable@kernel.org>
Fixes: 5157b8a5 ("Bluetooth: Fix initializing conn_params in scan phase")
Signed-off-by: Griffin Kroah-Hartman <griffin@kroah.com>
Reported-by: Yiwei Zhang <zhan4630@purdue.edu>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>