[CIFS] remove build warning

CC: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
diff --git a/fs/cifs/cifs_spnego.h b/fs/cifs/cifs_spnego.h
index f443f3b..05a34b1 100644
--- a/fs/cifs/cifs_spnego.h
+++ b/fs/cifs/cifs_spnego.h
@@ -41,6 +41,7 @@
 
 #ifdef __KERNEL__
 extern struct key_type cifs_spnego_key_type;
+extern struct key *cifs_get_spnego_key(struct cifsSesInfo *sesInfo);
 #endif /* KERNEL */
 
 #endif /* _CIFS_SPNEGO_H */