Bluetooth: Classic: SMP: Set BT_LINK_KEY_SC only if BT_KEYS_SC is set

The flag `BT_LINK_KEY_SC` of LK will also be set when derive LK from
LTK.
It is a incorrect behavior.

The flag `BT_LINK_KEY_SC` should only be set if the flag `BT_KEYS_SC`
of LTK has been set.

Signed-off-by: Lyle Zhu <lyle.zhu@nxp.com>