drm/i915: Don't leak in i915_gem_shmem_pread_slow()

It seems to me that we are leaking 'user_pages' in
drivers/gpu/drm/i915/i915_gem.c::i915_gem_shmem_pread_slow() if
read_cache_page_gfp() fails.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/i915/i915_gem.c

@@ -465,8 +465,10 @@ i915_gem_shmem_pread_slow(struct drm_device *dev,
 
 		page = read_cache_page_gfp(mapping, offset >> PAGE_SHIFT,
 					   GFP_HIGHUSER | __GFP_RECLAIMABLE);
-		if (IS_ERR(page))
-			return PTR_ERR(page);
+		if (IS_ERR(page)) {
+			ret = PTR_ERR(page);
+			goto out;
+		}
 
 		if (do_bit17_swizzling) {
 			slow_shmem_bit17_copy(page,