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/scsi/sd.c b/drivers/scsi/sd.c
index 69f542c..a69b155 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -676,7 +676,7 @@
  *	success as well). Returns a negated errno value in case of error.
  *
  *	Note: most ioctls are forward onto the block subsystem or further
- *	down in the scsi subsytem.
+ *	down in the scsi subsystem.
  **/
 static int sd_ioctl(struct inode * inode, struct file * filp, 
 		    unsigned int cmd, unsigned long arg)