openpowerlink: add patch to fix musl build

This commit adds a one-liner patch that fixes the build with musl of
the openpowerlink package, caused by a missing <sys/types.h>
include. The patch has been submitted upstream.

Fixes:

  http://autobuild.buildroot.net/results/8aff5f6d7bcab616129368c1fb22026bb164e454/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>