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/pata_sc1200.c b/drivers/ata/pata_sc1200.c
index 21ebc48..725a858 100644
--- a/drivers/ata/pata_sc1200.c
+++ b/drivers/ata/pata_sc1200.c
@@ -156,7 +156,7 @@
  *
  *	Called when the libata layer is about to issue a command. We wrap
  *	this interface so that we can load the correct ATA timings if
- *	neccessary.  Specifically we have a problem that there is only
+ *	necessary.  Specifically we have a problem that there is only
  *	one MWDMA/UDMA bit.
  */