CLEANUP: Do not use a fixed type for 'sizeof' in 'calloc'

Changes performed using the following coccinelle patch:

    @@
    type T;
    expression E;
    expression t;
    @@

    (
      t = calloc(E, sizeof(*t))
    |
    - t = calloc(E, sizeof(T))
    + t = calloc(E, sizeof(*t))
    )

Looking through the commit history, grepping for coccinelle shows that the same
replacement with a different patch was already performed in the past in commit
02779b6263a177b1e462e53db6eaf57bcda574bc.
diff --git a/src/fd.c b/src/fd.c
index c72dddd..d05df58 100644
--- a/src/fd.c
+++ b/src/fd.c
@@ -655,13 +655,13 @@
 	int p;
 	struct poller *bp;
 
-	if ((fdtab = calloc(global.maxsock, sizeof(struct fdtab))) == NULL)
+	if ((fdtab = calloc(global.maxsock, sizeof(*fdtab))) == NULL)
 		goto fail_tab;
 
 	if ((polled_mask = calloc(global.maxsock, sizeof(*polled_mask))) == NULL)
 		goto fail_polledmask;
 
-	if ((fdinfo = calloc(global.maxsock, sizeof(struct fdinfo))) == NULL)
+	if ((fdinfo = calloc(global.maxsock, sizeof(*fdinfo))) == NULL)
 		goto fail_info;
 
 	update_list.first = update_list.last = -1;