De-indent example code in rs6000-aix-tdep.c (ARI fix)

This patch de-indents the code provided as a comment explaining
how the code declaring the ld_info32_desc and ld_info64_desc globals
was generated. The intent is to avoid an ARI warning about a macro
not starting at column zero of the line.

gdb/ChangeLog:

        * rs6000-aix-tdep.c: De-indent some example code provided
        as a comment.