nimble/controller: Fix out of bound access to g_ble_ll_adv_sm
nimble/controller: Fix out of bound access to g_ble_ll_adv_sm

Instances are counted from 0 so last valid instance is
BLE_LL_ADV_INSTANCES - 1.

X-Original-Commit: 507e3d3f8f60dbd0245d0b408a9450a2f4479d46

apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble