Bluetooth: controller: fix comparision of unsigned int to 0

Fix the coverity issue CWE570, comparison of unsigned int to 0
in the definition of IS_SYNC_ISO_HANDLE

There is a potentially the same issue for IS_ADV_ISO_HANDLE,
fixed that as well

Signed-off-by: Andries Kruithof <andries.kruithof@nordicsemi.no>