Fix misspellings of "system", "controller", "interrupt" and "necessary".

Fix the various misspellings of "system", controller", "interrupt" and
"[un]necessary".

Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Signed-off-by: Adrian Bunk <bunk@kernel.org>
diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 64fee90..4a5849b 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -112,7 +112,7 @@
  * Different IV generation algorithms:
  *
  * plain: the initial vector is the 32-bit little-endian version of the sector
- *        number, padded with zeros if neccessary.
+ *        number, padded with zeros if necessary.
  *
  * essiv: "encrypted sector|salt initial vector", the sector number is
  *        encrypted with the bulk cipher using a salt as key. The salt