I reinstalled linux-headers-dt-kirkwood. Then, linux-headers-dt-kirkwood was uninstalled when I installed linux-headers-dt.
I tried to reinstall cryptodev-dkms at this point, and received the same error again.
$this->bbcode_second_pass_code('', '
(1/1) reinstalling cryptodev-dkms [####################################################] 100%
Creating symlink /var/lib/dkms/cryptodev/1.9/source ->
/usr/src/cryptodev-1.9
DKMS: add completed.
Error! echo
Your kernel headers for kernel 4.4.97-1-ARCH cannot be found at
/usr/lib/modules/4.4.97-1-ARCH/build or /usr/lib/modules/4.4.97-1-ARCH/source.
error: command failed to execute correctly
:: Running post-transaction hooks...
(1/2) Install DKMS modules
==> dkms install cryptodev/1.9 -k 4.16.9-2-ARCH
(2/2) Arming ConditionNeedsUpdate...
')