drm/i915: Switch kunmap() to take the page not vaddr

On converting from kunmap_atomic() to kunamp() one must remember the
latter takes the struct page, the former the vaddr.

Fixes: 48715f70 ("drm/i915: Avoid atomic context for error capture")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191125091409.1630385-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gpu_error.c

@@ -1045,7 +1045,7 @@ i915_error_object_create(struct drm_i915_private *i915,
 
 			s = kmap(page);
 			ret = compress_page(compress, s, dst);
-			kunmap(s);
+			kunmap(page);
 
 			drm_clflush_pages(&page, 1);