can: mcp251xfd: mcp251xfd_register_get_dev_id(): use correct length to read dev_id

The device ID register is 32 bits wide. The driver uses incorrectly
the size of a pointer to a u32 to calculate the length of the SPI
transfer. This results in a read of 2 registers on 64 bit platforms.
This is no problem on the Linux side, as the RX buffer of the SPI
transfer is large enough. In the mpc251xfd chip this results in the
read of an undocumented register. So far no problems were observed.

Fix the length of the SPI transfer to read the device ID register
only.

Link: https://lore.kernel.org/all/20220616094914.244440-1-mkl@pengutronix.de
Fixes: 55e5b97f ("can: mcp25xxfd: add driver for Microchip MCP25xxFD SPI CAN")
Reported-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c

@@ -1778,7 +1778,7 @@ mcp251xfd_register_get_dev_id(const struct mcp251xfd_priv *priv, u32 *dev_id,
 	xfer[0].len = sizeof(buf_tx->cmd);
 	xfer[0].speed_hz = priv->spi_max_speed_hz_slow;
 	xfer[1].rx_buf = buf_rx->data;
-	xfer[1].len = sizeof(dev_id);
+	xfer[1].len = sizeof(*dev_id);
 	xfer[1].speed_hz = priv->spi_max_speed_hz_fast;
 
 	mcp251xfd_spi_cmd_read_nocrc(&buf_tx->cmd, MCP251XFD_REG_DEVID);