Bluetooth: fix assignments on error variable err

Variable err is being initialized to zero and then later being
set to the error return from the call to hci_req_run_skb; hence
we can remove the redundant initialization to zero.

Also on two occassions err is not being set from the error return
from the call to hci_req_run_skb, so add these missing assignments.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>