calloc() and xcalloc() takes nmemb and then size

There are a handful more instances of this in compat/regex/ but they
are borrowed code taht we do not want to touch with a change that
really affects correctness, which this change is not.
Signed-off-by: NArjun Sreedharan <arjun024@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/for-each-ref.c

@@ -633,7 +633,7 @@ static void populate_value(struct refinfo *ref)
 	unsigned long size;
 	const unsigned char *tagged;
 
-	ref->value = xcalloc(sizeof(struct atom_value), used_atom_cnt);
+	ref->value = xcalloc(used_atom_cnt, sizeof(struct atom_value));
 
 	if (need_symref && (ref->flag & REF_ISSYMREF) && !ref->symref) {
 		unsigned char unused1[20];

imap-send.c

@@ -954,7 +954,7 @@ static struct imap_store *imap_open_store(struct imap_server_conf *srvc)
 
 	ctx = xcalloc(1, sizeof(*ctx));
 
-	ctx->imap = imap = xcalloc(sizeof(*imap), 1);
+	ctx->imap = imap = xcalloc(1, sizeof(*imap));
 	imap->buf.sock.fd[0] = imap->buf.sock.fd[1] = -1;
 	imap->in_progress_append = &imap->in_progress;