volser: Don't NULL conn right before assigning it

Don't do
   conn = NULL;
   conn = rx_newConnection();

and similar, equally pointless things.

Caught by clang-analyzer

Change-Id: I54d9ccd9f3910624b3289ce067a27622e29e4a34
Reviewed-on: http://gerrit.openafs.org/9199
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>