insque.3: Use sizeof consistently

Use ``sizeof`` consistently through all the examples in the following
way:

- Use the name of the variable instead of its type as argument for
  ``sizeof``.

	Rationale:
	https://www.kernel.org/doc/html/v5.8/process/coding-style.html#allocating-memory

Signed-off-by: Alejandro Colomar <colomar.6.4.3@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man3/insque.3

@@ -182,7 +182,7 @@ new_element(void)
 {
     struct element *e;
 
-    e = malloc(sizeof(struct element));
+    e = malloc(sizeof(*e));
     if (e == NULL) {
         fprintf(stderr, "malloc() failed\en");
         exit(EXIT_FAILURE);