bluetooth: host: Fixed missing guard for BT_SETTINGS_DEFINE

While linking with the IAR linker using generated linker scripts,
and with errors if unhandled sections are encountered, many of the
bluetooth tests failed because CONFIG_SETTINGS was not set.

The section that was not handled was
'._settings_handler_static.static.settings_handler_bt_ccc_'

Now it's only set if CONFIG_SETTINGS is set.

Signed-off-by: Lars-Ove Karlsson <lars-ove.karlsson@iar.com>