fix typos in comments and doc

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

scripts/kconfig/util.c

@@ -57,7 +57,7 @@ int file_write_dep(const char *name)
 }
 
 
-/* Allocate initial growable sting */
+/* Allocate initial growable string */
 struct gstr str_new(void)
 {
 	struct gstr gs;