flex_array: fix the panic when calling flex_array_alloc() without __GFP_ZERO

memset() is called with the wrong address and the kernel panics.
Signed-off-by: Changli Gao <xiaosuo@gmail.com>
Cc: Patrick McHardy <kaber@trash.net>
Acked-by: David Rientjes <rientjes@google.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/flex_array.c

@@ -99,7 +99,7 @@ struct flex_array *flex_array_alloc(int element_size, unsigned int total,
 	ret->element_size = element_size;
 	ret->total_nr_elements = total;
 	if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
-		memset(ret->parts[0], FLEX_ARRAY_FREE,
+		memset(&ret->parts[0], FLEX_ARRAY_FREE,
 						FLEX_ARRAY_BASE_BYTES_LEFT);
 	return ret;
 }