The issue is that sshd is not starting on your device.
I had a very similar issue and found out that albeit Dev mode was on, openssh was not installed (but that probably wasn't the real issue) and that in /usr/sbin/ there is sshd.disabled instead of sshd.

So I suggest you to first open Terminal and become root (devel-so, rootme) and check is /usr/sbin/sshd.disabled exists?
If so, rename it /usr/sbin/sshd and try

pkill -o sshd

and retry from Qt Creator to deploy. If it doesn't work, very probable, restart the phone, re-attach the USB cable in SDK mode and try again.

As suggested here, select PR1.2 from the list of devices in the Qt Wizard, create the SSH keys, put the SDK Mode password in the Qt Wizard fields when it asks for it and deploy the keys.

It should, hopefully, all work from there on.

Btw if /usr/sbin/sshd.disabled is not there, try first installing openssh:

apt-get install openssh

and check again. I did install openssh, but I think sshd was already there, but renamed sshd.disabled for some reason .