Fix spelling error (retreive for retrieve) in strings

Caught by Lintian analysis of the compiled binaries.

Reviewed-on: http://gerrit.openafs.org/8865
Reviewed-by: Ken Dreyer <ktdreyer@ktdreyer.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit 2e5ef04e24c89e846af7aae7da57a0b0f5e200c3)

Change-Id: Ied16661878edf39fb723e56c2ed997015e566b6e
Reviewed-on: http://gerrit.openafs.org/8869
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Paul Smeddle <paul.smeddle@gmail.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>