htmldocs: fix bio.c location

Commit f9c78b2b moved bio.c from fs/ to block/, but didn't
update the docbook location. Fix that up.
Signed-off-by: NJens Axboe <axboe@fb.com>

Documentation/DocBook/filesystems.tmpl

@@ -62,7 +62,7 @@
 !Efs/mpage.c
 !Efs/namei.c
 !Efs/buffer.c
-!Efs/bio.c
+!Eblock/bio.c
 !Efs/seq_file.c
 !Efs/filesystems.c
 !Efs/fs-writeback.c