bucoord: Remove dead initialisation

matchLength is set regardless of what the separator is, so we don't need
to provide a default value.

Caught by clang-analyzer

Change-Id: Iac8fe8db8832cf2b3347ec1bdacc7245bddf542b
Reviewed-on: http://gerrit.openafs.org/9257
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>