package/hans: fix build failures with high 'make -j' values

The top-level doesn't handle correctly the build dependencies
between .o files.

Since hans doesn't take too many time to build, just use MAKE1.

Fixes:
http://autobuild.buildroot.net/results/d14/d142f4a439d4d5fcc89865abde3e593c45ad5d96
http://autobuild.buildroot.net/results/28e/28ed230e40cc154db9274f9765085cd7f0eee85a
http://autobuild.buildroot.net/results/900/9008c3be3bcf46f0fc21a34f48e3cf9da1397d9a



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