Bluetooth: Remove unnecessary assignment in SMP

The smp variable in smp_conn_security is not used anywhere before the
smp = smp_chan_create() call in the smp_conn_security function so it
makes no sense to assign any other value to it before that.

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