Bluetooth: IAS: Fix coverity issue with IAS client lvl check

The check compared the levels against < BT_IAS_ALERT_LVL_NO_ALERT
which of course does not make sense given than the lvl_u8 is an
unsigned value that can never be < BT_IAS_ALERT_LVL_NO_ALERT.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>