spelling: s/usefull/useful/

Signed-off-by: Adrian Bunk <bunk@stusta.de>
diff --git a/Documentation/networking/sk98lin.txt b/Documentation/networking/sk98lin.txt
index 851fc97..f9d979e 100644
--- a/Documentation/networking/sk98lin.txt
+++ b/Documentation/networking/sk98lin.txt
@@ -245,7 +245,7 @@
 This parameters is only relevant if auto-negotiation for this port is 
 not set to "Sense". If auto-negotiation is set to "On", all three values
 are possible. If it is set to "Off", only "Full" and "Half" are allowed.
-This parameter is usefull if your link partner does not support all
+This parameter is useful if your link partner does not support all
 possible combinations.
 
 Flow Control