NFS: Fix typo in nomigration mount option

commit f02fee227e5f21981152850744a6084ff3fa94ee upstream.

The option was incorrectly masking off all other options.

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>