event: Fix a typo in the EVENT help

Fix the help message.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/Kconfig b/common/Kconfig
index 6591acd..6608a4f 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -577,7 +577,7 @@
 	help
 	  This enables sending and processing of events, to allow interested
 	  parties to be alerted when something happens. This is an attempt to
-	  step the flow of weak functions, hooks, functions in board_f.c
+	  stem the flow of weak functions, hooks, functions in board_f.c
 	  and board_r.c and the Kconfig options below.
 
 	  See doc/develop/event.rst for more information.