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/ubifs/xattr.c

@@ -313,7 +313,7 @@ static int setxattr(struct inode *host, const char *name, const void *value,
 	union ubifs_key key;
 	int err, type;
 
-	ubifs_assert(mutex_is_locked(&host->i_mutex));
+	ubifs_assert(inode_is_locked(host));
 
 	if (size > UBIFS_MAX_INO_DATA)
 		return -ERANGE;
@@ -550,7 +550,7 @@ int ubifs_removexattr(struct dentry *dentry, const char *name)
 
 	dbg_gen("xattr '%s', ino %lu ('%pd')", name,
 		host->i_ino, dentry);
-	ubifs_assert(mutex_is_locked(&host->i_mutex));
+	ubifs_assert(inode_is_locked(host));
 
 	err = check_namespace(&nm);
 	if (err < 0)