docs: Correctly spell Stephen Hemminger's name

This commit replaces "Steve" with the his real name, which is "Stephen".

Reported-by: Stephen Hemminger <[e-mail]>
Signed-off-by: Paul E. McKenney <[e-mail]>

Documentation/RCU/RTFP.txt

···
 	'It's entirely possible that the current user could be replaced
 	by RCU and/or seqlocks, and we could get rid of brlocks entirely.'
 	.
-	Steve Hemminger responds by replacing them with RCU.
+	Stephen Hemminger responds by replacing them with RCU.
 }
 }