NFS: Trim extra slash in v4 nfs_path

A NFSv4 mount of a subdirectory will show an extra slash (as in
'server://path'

) in proc's mountinfo which will not match the device name
and path.  This can cause problems for programs searching for the mount.
Fix this by checking for a leading slash in the dentry path, if so trim
away any trailing slashes in the device name.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>