ext4 crypto: enforce crypto policy restrictions on cross-renames

Thanks to Chao Yu <chao2.yu@samsung.com> for pointing out the need for
this check.

Change-Id: I957a4e4be043582972d3c8799f18826fc136d567
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Theodore Ts'o <tytso@google.com>