abitidy: extract code to get a comment node into a separate function

The piece of code to find the comment node for a node is replicated in 4
different places. This change consolidates this code in one place by
extracting it out into a function.

Bug: 238866030
Signed-off-by: Sid Nayyar <sidnayyar@google.com>
Change-Id: I91e84366033d640ff2ee7bb63598980b1a2acccf
1 file changed