hipe: Fix compilation with 'no_remove_comments'

To reproduce the error:
$ echo '-module(hello).' > hello.erl
$ erl
1> c(hello, [native,{hipe,[no_remove_comments]}]).
[...]
<HiPE (v 3.10.2.1)> Error: [hipe:834]: ERROR: {{case_clause,
                                                {icode_comment,call_ext_only}},
                                               [{hipe_icode,successors,1,
                                                 [{file,"hipe_icode.erl"},
                                                  {line,1444}]},
[...]