nfsd: avoid uninitialized variable warning

clang warns that 'contextlen' may be accessed without an initialization:

fs/nfsd/nfs4xdr.c:2911:9: error: variable 'contextlen' is uninitialized when used here [-Werror,-Wuninitialized]
                                                                contextlen);
                                                                ^~~~~~~~~~
fs/nfsd/nfs4xdr.c:2424:16: note: initialize the variable 'contextlen' to silence this warning
        int contextlen;
                      ^
                       = 0

Presumably this cannot happen, as FATTR4_WORD2_SECURITY_LABEL is
set if CONFIG_NFSD_V4_SECURITY_LABEL is enabled.
Adding another #ifdef like the other two in this function
avoids the warning.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4xdr.c

@@ -2420,8 +2420,10 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
 	__be32 status;
 	int err;
 	struct nfs4_acl *acl = NULL;
+#ifdef CONFIG_NFSD_V4_SECURITY_LABEL
 	void *context = NULL;
 	int contextlen;
+#endif
 	bool contextsupport = false;
 	struct nfsd4_compoundres *resp = rqstp->rq_resp;
 	u32 minorversion = resp->cstate.minorversion;
@@ -2906,12 +2908,14 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
 			*p++ = cpu_to_be32(NFS4_CHANGE_TYPE_IS_TIME_METADATA);
 	}
 
+#ifdef CONFIG_NFSD_V4_SECURITY_LABEL
 	if (bmval2 & FATTR4_WORD2_SECURITY_LABEL) {
 		status = nfsd4_encode_security_label(xdr, rqstp, context,
 								contextlen);
 		if (status)
 			goto out;
 	}
+#endif
 
 	attrlen = htonl(xdr->buf->len - attrlen_offset - 4);
 	write_bytes_to_xdr_buf(xdr->buf, attrlen_offset, &attrlen, 4);