A BO that's already swapped would be added back to the swap-LRU list
for example if its validation failed under high memory pressure. This
could later lead to swapping it out again and leaking previous swap
storage.

This commit adds a condition to prevent that from happening.

v2: Check page_flags instead of swap_storage
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org