busybox: S10mdev: fix module autoloading

Commit b4fc5a180c (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>
(cherry picked from commit 61717b7b3ef9c6c39f4adcbbb5dced3096f0ed08)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/busybox/S10mdev

@@ -9,7 +9,8 @@ case "$1" in
 	echo /sbin/mdev >/proc/sys/kernel/hotplug
 	/sbin/mdev -s
 	# coldplug modules
-	find /sys/ -name modalias -print0 | xargs -0 sort -u -z | xargs -0 modprobe -abq
+	find /sys/ -name modalias -print0 | xargs -0 sort -u | tr '\n' '\0' | \
+	    xargs -0 modprobe -abq
 	;;
   stop)
 	;;