libceph: add ceph_pg_pool_by_id()

"Lookup pool info by ID" function is hidden in osdmap.c.  Expose it to
the rest of libceph.

Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>
diff --git a/include/linux/ceph/osdmap.h b/include/linux/ceph/osdmap.h
index ebb8ec2..7f894a6 100644
--- a/include/linux/ceph/osdmap.h
+++ b/include/linux/ceph/osdmap.h
@@ -174,6 +174,9 @@
 extern int ceph_calc_pg_primary(struct ceph_osdmap *osdmap,
 				struct ceph_pg pgid);
 
+extern struct ceph_pg_pool_info *ceph_pg_pool_by_id(struct ceph_osdmap *map,
+						    u64 id);
+
 extern const char *ceph_pg_pool_name_by_id(struct ceph_osdmap *map, u64 id);
 extern int ceph_pg_poolid_by_name(struct ceph_osdmap *map, const char *name);