Subzero: With -asm-verbose, make the predecessor list more compact.

Instead of a comment like this:

  # preds=.Lfv_update_nonbon$split___114___115_0,.Lfv_update_nonbon$split___138___115_1

remove some redundancy and make the comment like this:

  # preds=$split___114___115_0,$split___138___115_1

This makes it slightly easier to read, and less likely to exceed 80 columns.

BUG= none
R=kschimpf@google.com

Review URL: https://codereview.chromium.org/1380323003 .