hotplug-dispatch: redirect output to /dev/null

hotplug-dispatch: redirect output to /dev/null

During the hotplug call via the procd, a list is first created with the files
in the hotplug.d directory. After that the scripts are then executed in
lexical order. However, if a script is deleted after the list has been
created, the following message is displayed on the tty console.

Command failed: Not found
/bin/sh: .: line 1: can't open '/etc/hotplug.d/ntp/25-travelmate_ntp': No such file or directory

So that the message is not displayed in the tty console the 'stderr' must be
redirected to '/dev/null'.

Signed-off-by: Florian Eckert <fe@dev.tdt.de>