soc/qcom: use struct_size over open coded arithmetic

Replace zero-length array with flexible-array member and make use
of the struct_size() helper in kzalloc(). For example:

struct apr_rx_buf {
	struct list_head node;
	int len;
	uint8_t buf[];
};

Make use of the struct_size() helper instead of an open-coded version
in order to avoid any potential type mistakes.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Minghao Chi (CGEL ZTE) <chi.minghao@zte.com.cn>

drivers/soc/qcom/apr.c

@@ -171,7 +171,7 @@ static int apr_callback(struct rpmsg_device *rpdev, void *buf,
 		return -EINVAL;
 	}
 
-	abuf = kzalloc(sizeof(*abuf) + len, GFP_ATOMIC);
+	abuf = kzalloc((struct_size(abuf, buf, len), GFP_ATOMIC);
 	if (!abuf)
 		return -ENOMEM;