busybox: S01mdev: fix module autoloading

Commit b4fc5a18 (package/busybox: support spaces in module aliases in
mdev) changed the mdev coldplugging to handle sysfs path elements and
modalias values containing spaces.  This unfortunately doesn't work as was
recently reported:

http://lists.busybox.net/pipermail/buildroot/2018-May/220903.html



The problem is that sort -z also expects the fields of the input files to be
zero terminated, which is not the case for modalias sysfs entries.

So drop the -z option to sort.  Spaces in modalias entries could be handled
with the xargs -d '\n' option, but that is unfortunately not supported by
the busybox applet.  Instead, use tr to convert newlines to zeros so we can
use xargs -0.

Reported-by: Daniel Palmer <daniel@0x0f.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>