nfsd: Fix display of the version string

The current display code assumes that v4 minor version 0 is tracked by
the call to nfsd_vers(). Now it is tracked by nfsd_minorversion(), and
so we need to adjust the display code.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>