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)
Status Name Job ID Coverage
  Build
passed build #180484

00:01:23

 
  Test
passed asan #180486

00:01:33

passed test #180485

00:01:17

 
  Manual
manual armv8 #180491
allowed to fail manual
manual flatpak #180487
allowed to fail manual
manual msan #180490
allowed to fail manual
manual ppc64le #180492
allowed to fail manual
manual tsan #180488
allowed to fail manual
manual ubsan #180489
allowed to fail manual
 
  Review
manual review #180493
allowed to fail manual
manual stop_review #180494
allowed to fail manual