l2c_csm: Use pL2CA_Error_Cb on error

Note that we only have two result codes, because the user only needs to
know whether it's during ConnectRsp or ConfigRsp (except for HIDH
retry), which we need further research.

Bug: 159815595
Tag: #refactor
Test: compile & verify basic functions working
Change-Id: I24aa7bf8487c9b2b69fc455cfdb52a7ec758b90b