Then I have no idea where it comes from. If you did everything I told you, then that message should not be there anymore. 
On the upside, it’s an irrelevant message and you can safely ignore it.
That should not have happened either, and may simply be down to some hardware-related randomness.
The only other advice I could give you — which in theory should speed up the boot process by about a second — is to modify the HOOKS line in your /etc/mkinitcpio.conf to a more modern one, using systemd instead of udev. The one with udev is actually an older and conservative configuration.
Currently, you have this… 
HOOKS=(base udev autodetect modconf kms block keyboard keymap filesystems fsck)
I would change that to…
HOOKS=(systemd autodetect microcode modconf kms keyboard sd-vconsole block filesystems fsck)
… and then run…
sudo mkinitcpio -P
… again.
P.S.: I strongly suspect that you’ve got a whole bunch of unattended .pacnew files lingering about on your system, given that the microcode HOOK was introduced at least three months ago, and your own /etc/mkinitcpio.conf doesn’t have it yet. And this then prompts me to recommend that you’d read the following short essay…