linux/string.h: fix comment typo

s/user/used/
Signed-off-by: NJeff Garzik <jgarzik@redhat.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

include/linux/string.h

 #ifndef _LINUX_STRING_H_
 #define _LINUX_STRING_H_
 
-/* We don't want strings.h stuff being user by user stuff by accident */
+/* We don't want strings.h stuff being used by user stuff by accident */
 
 #ifndef __KERNEL__
 #include <string.h>