package/openvmtools: don't use host library path

Set CUSTOM_PROCPS_LIBS to " " otherwise -L/lib is used by default.

Fixes:
http://autobuild.buildroot.net/results/bff/bff7d8f3ec19ce790f0c88a336d1007e1ff29836/



[Thomas: fix typo in commit log.]

Signed-off-by: Romain Naour <romain.naour@openwide.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>