spelling: s/usefull/useful/

Signed-off-by: Adrian Bunk <bunk@stusta.de>
diff --git a/drivers/net/sk98lin/skge.c b/drivers/net/sk98lin/skge.c
index 197edd7..a5f2b1e 100644
--- a/drivers/net/sk98lin/skge.c
+++ b/drivers/net/sk98lin/skge.c
@@ -2851,7 +2851,7 @@
  * Description:
  *	This function is called if an ioctl is issued on the device.
  *	There are three subfunction for reading, writing and test-writing
- *	the private MIB data structure (usefull for SysKonnect-internal tools).
+ *	the private MIB data structure (useful for SysKonnect-internal tools).
  *
  * Returns:
  *	0, if everything is ok