dm: core: fix a typo in help text

Signed-off-by: Sergei Antonov <saproj@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/dm.c b/cmd/dm.c
index eb40f08..218be85 100644
--- a/cmd/dm.c
+++ b/cmd/dm.c
@@ -87,7 +87,7 @@
 	"dm drivers       Dump list of drivers with uclass and instances\n"
 	DM_MEM_HELP
 	"dm static        Dump list of drivers with static platform data\n"
-	"dn tree          Dump tree of driver model devices ('*' = activated)\n"
+	"dm tree          Dump tree of driver model devices ('*' = activated)\n"
 	"dm uclass        Dump list of instances for each uclass"
 	;
 #endif