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/fs/hpfs/Kconfig b/fs/hpfs/Kconfig
index 56aa033..2b36dc6 100644
--- a/fs/hpfs/Kconfig
+++ b/fs/hpfs/Kconfig
@@ -9,7 +9,7 @@
 	  write files to an OS/2 HPFS partition on your hard drive. OS/2
 	  floppies however are in regular MSDOS format, so you don't need this
 	  option in order to be able to read them. Read
-	  <file:Documentation/filesystems/hpfs.txt>.
+	  <file:Documentation/filesystems/hpfs.rst>.
 
 	  To compile this file system support as a module, choose M here: the
 	  module will be called hpfs.  If unsure, say N.