volser: set error, not code, before rfail

volser: set error, not code, before rfail

The rfail cleanup handler overwrites 'code' ~unconditionally, but
does use an existing 'error' value if present.  Since the intent
is to return failure to the caller, preserve the code in the error
variable and do so.

FIXES 131897

Change-Id: I25db2f9ad75a5b856626d39d35f97a09f26bd7a9
Reviewed-on: http://gerrit.openafs.org/12108
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>