can: hi311x: fix a signedness bug in hi3110_cmd()

The hi3110_cmd() is supposed to return zero on success and negative
error codes on failure, but it was accidentally declared as a u8 when
it needs to be an int type.

Fixes: 57e83fb9 ("can: hi311x: Add Holt HI-311x CAN driver")
Link: https://lore.kernel.org/r/20210729141246.GA1267@kiliSigned-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/spi/hi311x.c

@@ -218,7 +218,7 @@ static int hi3110_spi_trans(struct spi_device *spi, int len)
 	return ret;
 }
 
-static u8 hi3110_cmd(struct spi_device *spi, u8 command)
+static int hi3110_cmd(struct spi_device *spi, u8 command)
 {
 	struct hi3110_priv *priv = spi_get_drvdata(spi);