drivers/net/can: Correct NULL test

Test the just-allocated value for NULL rather than some other value.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
expression x,y;
statement S;
@@

x = \(kmalloc\|kcalloc\|kzalloc\)(...);
(
if ((x) == NULL) S
|
if (
-   y
+   x
       == NULL)
 S
)
// </smpl>
Signed-off-by: NJulia Lawall <julia@diku.dk>
Acked-by: NOliver Hartkopp <oliver@hartkopp.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/can/mcp251x.c

@@ -990,7 +990,7 @@ static int __devinit mcp251x_can_probe(struct spi_device *spi)
 			goto error_tx_buf;
 		}
 		priv->spi_rx_buf = kmalloc(SPI_TRANSFER_BUF_LEN, GFP_KERNEL);
-		if (!priv->spi_tx_buf) {
+		if (!priv->spi_rx_buf) {
 			ret = -ENOMEM;
 			goto error_rx_buf;
 		}