gpu: drm: mgag200: mgag200_main:- Handle error from pci_iomap

Here, pci_iomap can fail, handle this case and return -ENOMEM.
Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1483443027-13444-1-git-send-email-arvind.yadav.cs@gmail.com

drivers/gpu/drm/mgag200/mgag200_main.c

@@ -145,6 +145,8 @@ static int mga_vram_init(struct mga_device *mdev)
 	}
 
 	mem = pci_iomap(mdev->dev->pdev, 0, 0);
+	if (!mem)
+		return -ENOMEM;
 
 	mdev->mc.vram_size = mga_probe_vram(mdev, mem);