can: usb_8dev: Fix memory leak of priv->cmd_msg_buffer

commit 7c42631376306fb3f34d51fda546b50a9b6dd6ec upstream.

The priv->cmd_msg_buffer is allocated in the probe function, but never
kfree()ed. This patch converts the kzalloc() to resource-managed
kzalloc.

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Willy Tarreau <w@1wt.eu>