nimble/mesh: Fix failed provisioning response
nimble/mesh: Fix failed provisioning response

Found during PTS testing. With this patch following test cases pass:

MESH/NODE/PROV/UPD/BV-10-C
MESH/NODE/PROV/BI-02-C

X-Original-Commit: e992ec3b022c4e9ad95e13be6e0ab80b3a623e9d

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