docs: filesystems: fix renamed references

Some filesystem references got broken by a previous patch
series I submitted. Address those.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Acked-by: David Sterba <dsterba@suse.com> # fs/affs/Kconfig
Link: https://lore.kernel.org/r/57318c53008dbda7f6f4a5a9e5787f4d37e8565a.1586881715.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/filesystems/dax.txt b/Documentation/filesystems/dax.txt
index 6797294..735f385 100644
--- a/Documentation/filesystems/dax.txt
+++ b/Documentation/filesystems/dax.txt
@@ -74,7 +74,7 @@
 exposure of uninitialized data through mmap.
 
 These filesystems may be used for inspiration:
-- ext2: see Documentation/filesystems/ext2.txt
+- ext2: see Documentation/filesystems/ext2.rst
 - ext4: see Documentation/filesystems/ext4/
 - xfs:  see Documentation/admin-guide/xfs.rst
 
diff --git a/Documentation/filesystems/dnotify.txt b/Documentation/filesystems/dnotify.txt
index 1515688..08d575e 100644
--- a/Documentation/filesystems/dnotify.txt
+++ b/Documentation/filesystems/dnotify.txt
@@ -67,4 +67,4 @@
 NOTE
 ----
 Beginning with Linux 2.6.13, dnotify has been replaced by inotify.
-See Documentation/filesystems/inotify.txt for more information on it.
+See Documentation/filesystems/inotify.rst for more information on it.
diff --git a/Documentation/filesystems/ramfs-rootfs-initramfs.rst b/Documentation/filesystems/ramfs-rootfs-initramfs.rst
index 6c576e2..3fddacc 100644
--- a/Documentation/filesystems/ramfs-rootfs-initramfs.rst
+++ b/Documentation/filesystems/ramfs-rootfs-initramfs.rst
@@ -71,7 +71,7 @@
 
 A ramfs derivative called tmpfs was created to add size limits, and the ability
 to write the data to swap space.  Normal users can be allowed write access to
-tmpfs mounts.  See Documentation/filesystems/tmpfs.txt for more information.
+tmpfs mounts.  See Documentation/filesystems/tmpfs.rst for more information.
 
 What is rootfs?
 ---------------
diff --git a/Documentation/filesystems/sysfs.rst b/Documentation/filesystems/sysfs.rst
index 290891c..ab0f779 100644
--- a/Documentation/filesystems/sysfs.rst
+++ b/Documentation/filesystems/sysfs.rst
@@ -20,7 +20,7 @@
 linkages between them to userspace.
 
 sysfs is tied inherently to the kobject infrastructure. Please read
-Documentation/kobject.txt for more information concerning the kobject
+Documentation/core-api/kobject.rst for more information concerning the kobject
 interface.