watchdog: lenovo_se30_wdt: Fix possible devm_ioremap() NULL pointer dereference in lenovo_se30_wdt_probe()

devm_ioremap() returns NULL on error. Currently, lenovo_se30_wdt_probe()
does not check for this case, which results in a NULL pointer
dereference.

Add NULL check after devm_ioremap() to prevent this issue.

Fixes: c284153a2c55 ("watchdog: lenovo_se30_wdt: Watchdog driver for Lenovo SE30 platform")
Signed-off-by: Henry Martin <[e-mail]>
Reviewed-by: Guenter Roeck <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Guenter Roeck <[e-mail]>
Signed-off-by: Wim Van Sebroeck <[e-mail]>

drivers/watchdog/lenovo_se30_wdt.c

···
 		return -EBUSY;
 
 	priv->shm_base_addr = devm_ioremap(dev, base_phys, SHM_WIN_SIZE);
+	if (!priv->shm_base_addr)
+		return -ENOMEM;
 
 	priv->wdt_cfg.mod = WDT_MODULE;
 	priv->wdt_cfg.idx = WDT_CFG_INDEX;