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/hpfs/dir.c

@@ -33,7 +33,7 @@ static loff_t hpfs_dir_lseek(struct file *filp, loff_t off, int whence)
 	if (whence == SEEK_DATA || whence == SEEK_HOLE)
 		return -EINVAL;
 
-	mutex_lock(&i->i_mutex);
+	inode_lock(i);
 	hpfs_lock(s);
 
 	/*pr_info("dir lseek\n");*/
@@ -48,12 +48,12 @@ static loff_t hpfs_dir_lseek(struct file *filp, loff_t off, int whence)
 ok:
 	filp->f_pos = new_off;
 	hpfs_unlock(s);
-	mutex_unlock(&i->i_mutex);
+	inode_unlock(i);
 	return new_off;
 fail:
 	/*pr_warn("illegal lseek: %016llx\n", new_off);*/
 	hpfs_unlock(s);
-	mutex_unlock(&i->i_mutex);
+	inode_unlock(i);
 	return -ESPIPE;
 }