video: imsttfb: check for ioremap() failures

We should check if ioremap() were to somehow fail in imsttfb_probe() and
handle the unwinding of the resources allocated here properly.

Ideally if anyone cares about this driver (it's for a PowerMac era PCI
display card), they wouldn't even be using fbdev anymore. Or the devm_*
apis could be used, but that's just extra work for diminishing
returns...

Cc: Finn Thain <[e-mail]>
Cc: Bartlomiej Zolnierkiewicz <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/video/fbdev/imsttfb.c

···
 	struct imstt_par *par;
 	struct fb_info *info;
 	struct device_node *dp;
+	int ret = -ENOMEM;
 	
 	dp = pci_device_to_OF_node(pdev);
 	if(dp)
···
 		default:
 			printk(KERN_INFO "imsttfb: Device 0x%x unknown, "
 					 "contact maintainer.\n", pdev->device);
-			release_mem_region(addr, size);
-			framebuffer_release(info);
-			return -ENODEV;
+			ret = -ENODEV;
+			goto error;
 	}
 
 	info->fix.smem_start = addr;
 	info->screen_base = (__u8 *)ioremap(addr, par->ramdac == IBM ?
 					    0x400000 : 0x800000);
+	if (!info->screen_base)
+		goto error;
 	info->fix.mmio_start = addr + 0x800000;
 	par->dc_regs = ioremap(addr + 0x800000, 0x1000);
+	if (!par->dc_regs)
+		goto error;
 	par->cmap_regs_phys = addr + 0x840000;
 	par->cmap_regs = (__u8 *)ioremap(addr + 0x840000, 0x1000);
+	if (!par->cmap_regs)
+		goto error;
 	info->pseudo_palette = par->palette;
 	init_imstt(info);
 
 	pci_set_drvdata(pdev, info);
 	return 0;
+
+error:
+	if (par->dc_regs)
+		iounmap(par->dc_regs);
+	if (info->screen_base)
+		iounmap(info->screen_base);
+	release_mem_region(addr, size);
+	framebuffer_release(info);
+	return ret;
 }
 
 static void imsttfb_remove(struct pci_dev *pdev)