poppler: fix build with openjpeg

The openjpeg version we have in Buildroot is v1, not v2.

Fixes:
http://autobuild.buildroot.net/results/e17/e17193604956cc61d47a9913632144601ef72656/
http://autobuild.buildroot.net/results/6b9/6b9d4ce15f54683670af3132ab21a053d9853e6c/



Signed-off-by: Peter Korsgaard <peter@korsgaard.com>