drm/imagination: fix off by one in pvr_vm_mips_init() error handling

If the call to vmap() fails the "page_nr" is one element beyond the end
of the mips_data->pt_dma_addr[] and mips_data->pt_pages[] arrays.

The way that this is traditionally written is that we clean up the
partial loop iteration before the goto and then we can say
while (--i >= 0).  At that point we know that all the elements thus
far are initialized so we don't need to have NULL checks.

Fixes: 927f3e02 ("drm/imagination: Implement MIPS firmware processor and MMU support")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Frank Binns <frank.binns@imgtec.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/a2d3210b-290f-4397-9c3e-efdcca94d8ac@moroto.mountain

drivers/gpu/drm/imagination/pvr_vm_mips.c

@@ -57,6 +57,7 @@ pvr_vm_mips_init(struct pvr_device *pvr_dev)
 							       PAGE_SIZE, DMA_TO_DEVICE);
 		if (dma_mapping_error(dev, mips_data->pt_dma_addr[page_nr])) {
 			err = -ENOMEM;
+			__free_page(mips_data->pt_pages[page_nr]);
 			goto err_free_pages;
 		}
 	}
@@ -79,12 +80,10 @@ pvr_vm_mips_init(struct pvr_device *pvr_dev)
 	return 0;
 
 err_free_pages:
-	for (; page_nr >= 0; page_nr--) {
-		if (mips_data->pt_dma_addr[page_nr])
+	while (--page_nr >= 0) {
 		dma_unmap_page(from_pvr_device(pvr_dev)->dev,
 			       mips_data->pt_dma_addr[page_nr], PAGE_SIZE, DMA_TO_DEVICE);
 
-		if (mips_data->pt_pages[page_nr])
 		__free_page(mips_data->pt_pages[page_nr]);
 	}