NFS: Give "flavor" an initial value to fix a compile warning

The previous patch introduces a compile warning by not assigning an initial
value to the "flavor" variable.  This could only be a problem if the server
returns a supported secflavor list of length zero, but it's better to
fix this before it's ever hit.

Signed-off-by: Anna Schumaker <bjschuma@netapp.com>
Acked-by: Weston Andros Adamson <dros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>