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/ata/libata-sff.c b/drivers/ata/libata-sff.c
index f9e4cd5..8227c45 100644
--- a/drivers/ata/libata-sff.c
+++ b/drivers/ata/libata-sff.c
@@ -856,7 +856,7 @@
  *	@pdev: PCI device
  *
  *	Some PCI ATA devices report simplex mode but in fact can be told to
- *	enter non simplex mode. This implements the neccessary logic to
+ *	enter non simplex mode. This implements the necessary logic to
  *	perform the task on such devices. Calling it on other devices will
  *	have -undefined- behaviour.
  */