If the kernel log mentions that a device is not configured, it isn't usually an indication of user error.
All supported drivers are part of the GENERIC kernel image, there are no externally loaded drivers, so there isn't any configuration required on your part.
The message typically means the device is unsupported, none of the available drivers are able to attach to it.. the exact reasons for this are dependent on the device.
Unfortunately a lot of those internal card readers are unsupported, except for some lucky users with
sdhc(4) SD card readers.. or internal multicard readers attached to the USB bus.
I can't be completely sure without a dmesg, but this is most likely to be the case.
OpenBSD's device support has improved quite a bit over the years, but, they need access to machines to write drivers.. and if nobody is particularly interested in writing a driver, it won't be done. There is also the issue of available documentation, TI is a common manufacture of these multicard readers.. but surely not the only one, which would make the job much more complicated.
Try finding an external USB device if the data on the card is important, or use a different computer/OS temporarily.
Good luck,