wayland/data-device: Use correct selection type to get mime types

When primary_offer_receive checks if the requested mime_type is supported,
it should check against the list of mime-types supported by the
primary-selection, instead of the list for the clipboard.

This fixes primary selection copy paste from X11 apps to Wayland apps
not working.

Fixes: GNOME/mutter#702
8 jobs for !725 with wayland-primary-sel-fix in 17 minutes and 46 seconds (queued for 2 seconds)
detached
Status Job ID Name Coverage
  Review
passed #391569
check-commit-log

00:00:28

 
  Build
passed #391765
build-mutter

00:14:43

passed #391766
build-without-native-backend

00:04:38

failed #391752
build-mutter

00:00:54

failed #391570
build-mutter

00:00:49

failed #391571
build-without-native-backend

00:00:43

 
  Test
passed #391573
can-build-gnome-shell

00:01:51

passed #391572
test-mutter

00:02:34