bucoord: Remove dead initialisation

offset is simply used as a copy of nextOffset for the GetText
function call. We don't need to initialise it to 0 at the start of
the loop (and arguably, as it is passed to the function by value,
we could just remove the copy entirely)

Caught by clang-analyzer

Change-Id: I137ea3ba1ff44d94b90287d9735db69d6ff8717d
Reviewed-on: http://gerrit.openafs.org/9249
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>