fs: move fscrypt keyring destruction to after ->put_super

btrfs has a variety of asynchronous things we do with inodes that can
potentially last until ->put_super, when we shut everything down and
clean up all of our async work.  Due to this we need to move
fscrypt_destroy_keyring() to after ->put_super, otherwise we get
warnings about still having active references on the master key.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Neal Gompa <neal@gompa.dev>
Link: https://lore.kernel.org/r/20231227171429.9223-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>