datetime: Use accessible-description instead of -name for Hour & Minute

In my testing, default orca didn't seem to read the "Hour" or "Minute"
words when we used accessible-name but it does work with
accessible-description.

This is the only place we used accessible-name in gnome-control-center
but we use accessible-description in a few other places.
11 jobs for datetime-a11y in 2 minutes and 56 seconds (queued for 2 seconds)