drm/vgem: off by one in vgem_gem_fault()

If page_offset is == num_pages then we end up reading beyond the end of
obj->pages[].

Fixes: af33a9190d02 ("drm/vgem: Enable dmabuf import interfaces")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180703122921.brlfxl4vx2ybvrd2@kili.mountain

drivers/gpu/drm/vgem/vgem_drv.c

@@ -74,7 +74,7 @@ static vm_fault_t vgem_gem_fault(struct vm_fault *vmf)
 
 	num_pages = DIV_ROUND_UP(obj->base.size, PAGE_SIZE);
 
-	if (page_offset > num_pages)
+	if (page_offset >= num_pages)
 		return VM_FAULT_SIGBUS;
 
 	mutex_lock(&obj->pages_lock);