use CALLOC_ARRAY

Add and apply a semantic patch for converting code that open-codes
CALLOC_ARRAY to use it instead.  It shortens the code and infers the
element size automatically.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/range-diff.c b/range-diff.c
index a3cc7c9..116fb07 100644
--- a/range-diff.c
+++ b/range-diff.c
@@ -96,7 +96,7 @@ static int read_patches(const char *range, struct string_list *list,
 				string_list_append(list, buf.buf)->util = util;
 				strbuf_reset(&buf);
 			}
-			util = xcalloc(sizeof(*util), 1);
+			CALLOC_ARRAY(util, 1);
 			if (get_oid(p, &util->oid)) {
 				error(_("could not parse commit '%s'"), p);
 				free(util);