Documentation: Fix multiple typo in Documentation

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/Documentation/device-mapper/dm-raid.txt b/Documentation/device-mapper/dm-raid.txt
index 2a8c113..946c733 100644
--- a/Documentation/device-mapper/dm-raid.txt
+++ b/Documentation/device-mapper/dm-raid.txt
@@ -28,7 +28,7 @@
   raid6_nc	RAID6 N continue
 		- rotating parity N (right-to-left) with data continuation
 
-  Refererence: Chapter 4 of
+  Reference: Chapter 4 of
   http://www.snia.org/sites/default/files/SNIA_DDF_Technical_Position_v2.0.pdf
 
 <#raid_params>: The number of parameters that follow.