[PATCH] can: etas_es58x: initialize rx_event_msg before calling es58x_check_msg_len()

[Vincent Mailhol <mailhol.vincent@wanadoo.fr>]

Function es58x_fd_rx_event() invokes the es58x_check_msg_len() macro:
| 	ret = es58x_check_msg_len(es58x_dev->dev, *rx_event_msg, msg_len);
While doing so, it deferences an uninitialized variable: *rx_event_msg.

This is actually harmless because es58x_check_msg_len() only uses
preprocessors macro (sizeof() and __stringify()) on
*rx_event_msg. c.f. [1].

Nonetheless, this pattern is confusing so the lines are reordered to
make sure that rx_event_msg is correctly initialized.

This patch also fixes a false positive warning reported by cppcheck:

| cppcheck possible warnings: (new ones prefixed by >>, may not be real problems)
|
|     In file included from drivers/net/can/usb/etas_es58x/es58x_fd.c:
|  >> drivers/net/can/usb/etas_es58x/es58x_fd.c:174:8: warning: Uninitialized variable: rx_event_msg [uninitvar]
|      ret = es58x_check_msg_len(es58x_dev->dev, *rx_event_msg, msg_len);
|            ^

[1] https://elixir.bootlin.com/linux/latest/source/drivers/net/can/usb/etas_es58x/es58x_core.h#L467

Reported-by: kernel test robot <yujie.liu@intel.com>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
---
As discussed in
https://lore.kernel.org/linux-can/20220302130423.ddd2ulldffpo5lb2@pengutronix.de/T/#u,
no need to backport this patch because this is not a fix.

@Yujie Liu: I added the "Reported-by: kernel test robot". This being a
false positive, let me know if you would like to remove the tag in
order not to mess with you statistics.
---
 drivers/net/can/usb/etas_es58x/es58x_fd.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/net/can/usb/etas_es58x/es58x_fd.c b/drivers/net/can/usb/etas_es58x/es58x_fd.c
index 88d2540abbbe..c97ffa71fd75 100644
--- a/drivers/net/can/usb/etas_es58x/es58x_fd.c
+++ b/drivers/net/can/usb/etas_es58x/es58x_fd.c
@@ -173,12 +173,11 @@ static int es58x_fd_rx_event_msg(struct net_device *netdev,
 	const struct es58x_fd_rx_event_msg *rx_event_msg;
 	int ret;
 
+	rx_event_msg = &es58x_fd_urb_cmd->rx_event_msg;
 	ret = es58x_check_msg_len(es58x_dev->dev, *rx_event_msg, msg_len);
 	if (ret)
 		return ret;
 
-	rx_event_msg = &es58x_fd_urb_cmd->rx_event_msg;
-
 	return es58x_rx_err_msg(netdev, rx_event_msg->error_code,
 				rx_event_msg->event_code,
 				get_unaligned_le64(&rx_event_msg->timestamp));
-- 
2.34.1