init: add an init_umount helper

Like ksys_umount, but takes a kernel pointer for the destination path.
Switch over the umount in the init code, which just happen to work due to
the implicit set_fs(KERNEL_DS) during early init right now.

Signed-off-by: Christoph Hellwig <hch@lst.de>

fs/internal.h

@@ -92,6 +92,7 @@ extern void dissolve_on_fput(struct vfsmount *);
 
 int path_mount(const char *dev_name, struct path *path,
 		const char *type_page, unsigned long flags, void *data_page);
+int path_umount(struct path *path, int flags);
 
 /*
  * fs_struct.c