perl: fix build on big endian arch

see http://autobuild.buildroot.org/results/3a1/3a1c2f0bc802d3cec26ffd4ded8f5c04473a3d4b/build-end.log

Signed-off-by: Francois Perrad <francois.perrad@gadz.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>