libceph: eliminate sparse warnings

Eliminate most of the problems in the libceph code that cause sparse
to issue warnings.
    - Convert functions that are never referenced externally to have
      static scope.
    - Pass NULL rather than 0 for a pointer argument in one spot in
      ceph_monc_delete_snapid()

This partially resolves:
    http://tracker.ceph.com/issues/4184

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
diff --git a/net/ceph/crypto.c b/net/ceph/crypto.c
index af14cb4..6e7a236 100644
--- a/net/ceph/crypto.c
+++ b/net/ceph/crypto.c
@@ -423,7 +423,8 @@
 	}
 }
 
-int ceph_key_instantiate(struct key *key, struct key_preparsed_payload *prep)
+static int ceph_key_instantiate(struct key *key,
+				struct key_preparsed_payload *prep)
 {
 	struct ceph_crypto_key *ckey;
 	size_t datalen = prep->datalen;
@@ -458,12 +459,12 @@
 	return ret;
 }
 
-int ceph_key_match(const struct key *key, const void *description)
+static int ceph_key_match(const struct key *key, const void *description)
 {
 	return strcmp(key->description, description) == 0;
 }
 
-void ceph_key_destroy(struct key *key) {
+static void ceph_key_destroy(struct key *key) {
 	struct ceph_crypto_key *ckey = key->payload.data;
 
 	ceph_crypto_key_destroy(ckey);