builder: Fix multilib compile failure

builder: Fix multilib compile failure

The last commit introduced a build failure in the multilib case:

| WARNING: /media/data1/build1/poky/build/tmp/work/x86-pokymllib32-linux/lib32-builder/0.1-r6/temp/run.do_install.781:1 exit 1 from
|   chown lib32-builder.lib32-builder /media/data1/build1/poky/build/tmp/work/x86-pokymllib32-linux/lib32-builder/0.1-r6/image/etc/mini_x/session.d/builder_hob_start.sh

so fix the chown to use the correct user.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>