can: mpc5xxx_can: check of_iomap return before use

of_iomap() can return NULL so that return needs to be checked and NULL
treated as failure. While at it also take care of the missing
of_node_put() in the error path.
Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Fixes: commit afa17a50 ("net/can: add driver for mscan family & mpc52xx_mscan")
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/mscan/mpc5xxx_can.c

@@ -86,6 +86,11 @@ static u32 mpc52xx_can_get_clock(struct platform_device *ofdev,
 		return 0;
 	}
 	cdm = of_iomap(np_cdm, 0);
+	if (!cdm) {
+		of_node_put(np_cdm);
+		dev_err(&ofdev->dev, "can't map clock node!\n");
+		return 0;
+	}
 
 	if (in_8(&cdm->ipb_clk_sel) & 0x1)
 		freq *= 2;