package/openlayers: do not rely on install -D -t

Use a more standard $(INSTALL) -D solution instead of -D -t, as it
causes some failures in the autobuilders.

Fixes:

  http://autobuild.buildroot.net/results/b473c44ae953dec3e4f88c4e363fb1a84b5e0dc8/



Signed-off-by: Thomas Claveirole <thomas.claveirole@green-communications.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>