Fix translation of bs_add's fail label to Icode

[Kostis Sagonas]

Please fetch

     git fetch git://github.com/kostis/otp.git bs_add-fail-labels

The change fixes a bug in the translation of 'bs_add' BEAM instruction 
to HiPE's Icode representation and can be pushed immediately to 'dev'.
When these instructions appeared in a guard context the previous 
translation was obviously buggy.

Kostis