erlang-p1-xml: Fix host dependencies variable name

This should fix the error reported by autobuild:
http://autobuild.buildroot.net/results/63c/63c63b2578e9f6ad71cbea82b987c128305cdab4/



Signed-off-by: Johan Oudinet <johan.oudinet@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>