NFS: Fix a few constant_table array definitions

nfs_vers_tokens, nfs_xprt_protocol_tokens, and nfs_secflavor_tokens were
all missing an empty item at the end of the array, allowing
lookup_constant() to potentially walk off the end and trigger and oops.

Reported-by: Olga Kornievskaia <aglo@umich.edu>
Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Fixes: e38bb23 ("NFS: Convert mount option parsing to use functionality from fs_parser.h")
Cc: stable@vger.kernel.org # v5.6
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/fs_context.c

@@ -190,6 +190,7 @@ static const struct constant_table nfs_vers_tokens[] = {
 	{ "4.0",	Opt_vers_4_0 },
 	{ "4.1",	Opt_vers_4_1 },
 	{ "4.2",	Opt_vers_4_2 },
+	{}
 };
 
 enum {
@@ -202,13 +203,14 @@ enum {
 	nr__Opt_xprt
 };
 
-static const struct constant_table nfs_xprt_protocol_tokens[nr__Opt_xprt] = {
+static const struct constant_table nfs_xprt_protocol_tokens[] = {
 	{ "rdma",	Opt_xprt_rdma },
 	{ "rdma6",	Opt_xprt_rdma6 },
 	{ "tcp",	Opt_xprt_tcp },
 	{ "tcp6",	Opt_xprt_tcp6 },
 	{ "udp",	Opt_xprt_udp },
 	{ "udp6",	Opt_xprt_udp6 },
+	{}
 };
 
 enum {
@@ -239,6 +241,7 @@ static const struct constant_table nfs_secflavor_tokens[] = {
 	{ "spkm3i",	Opt_sec_spkmi },
 	{ "spkm3p",	Opt_sec_spkmp },
 	{ "sys",	Opt_sec_sys },
+	{}
 };
 
 /*