wrappers for ->i_mutex access

parallel to mutex_{lock,unlock,trylock,is_locked,lock_nested},
inode_foo(inode) being mutex_foo(&inode->i_mutex).

Please, use those for access to ->i_mutex; over the coming cycle
->i_mutex will become rwsem, with ->lookup() done with it held
only shared.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/ceph/cache.c

@@ -197,7 +197,7 @@ void ceph_fscache_register_inode_cookie(struct ceph_fs_client* fsc,
 		return;
 
 	/* Avoid multiple racing open requests */
-	mutex_lock(&inode->i_mutex);
+	inode_lock(inode);
 
 	if (ci->fscache)
 		goto done;
@@ -207,7 +207,7 @@ void ceph_fscache_register_inode_cookie(struct ceph_fs_client* fsc,
 					     ci, true);
 	fscache_check_consistency(ci->fscache);
 done:
-	mutex_unlock(&inode->i_mutex);
+	inode_unlock(inode);
 
 }