treewide: Fix typo in Documentation/DocBook

This patch fix spelling typo in Documentation/DocBook.
It is because .html and .xml files are generated by make htmldocs,
I have to fix a typo within the source files.

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/fs/buffer.c b/fs/buffer.c
index 6024877..a20f2eb 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -3086,7 +3086,7 @@
  * until the buffer gets unlocked).
  *
  * ll_rw_block sets b_end_io to simple completion handler that marks
- * the buffer up-to-date (if approriate), unlocks the buffer and wakes
+ * the buffer up-to-date (if appropriate), unlocks the buffer and wakes
  * any waiters. 
  *
  * All of the buffers must be for the same device, and must also be a