cocci: allow xcalloc(1, size)

Allocating a pre-cleared single element is quite common and it is
misleading to use CALLOC_ARRAY(); these allocations that would be
affected without this change are not allocating an array.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/coccinelle/array.cocci

@@ -92,7 +92,7 @@ expression n;
 @@
 type T;
 T *ptr;
-expression n;
+expression n != 1;
 @@
 - ptr = xcalloc(n, \( sizeof(*ptr) \| sizeof(T) \) )
 + CALLOC_ARRAY(ptr, n)