busybox: fix mdev.conf

busybox: fix mdev.conf

mdev does not set "/dev/snd" and "/dev/input" group and permission
propery, because with commit c3cf1e30a3022453311a7e9fe11d94c7a381640e
(May 2013!) the behavior of mdev has changed.

The device name is now taken directly from the uevent file and does no
longer match the old rule.

Fix the rules for "/dev/snd" and "/dev/input" according to the example
given in [1].

[1] http://lists.busybox.net/pipermail/busybox/2015-February/082297.html

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>