beaglebone: s/devicetrees/devicetree/
beaglebone: s/devicetrees/devicetree/

The package was named differently in the 'dylan' branch, fix it to work on master as well.

Signed-off-by: Koen Kooi <42e3d96910f922bdd7dd1805fe3f8aff634f391d@dominion.thruhere.net>
koenkooi/meta-beagleboard,koenkooi/meta-beagleboard