Prevent duplicate kernel message in journal

OpenBMC uses busybox which uses klogd which causes duplicate
kernel messages to show up in the journal due to syslog.
This override prevents journald from reading from kmsg so
only one instance of the kernel messages will show up in
journald instead of the two of each currently put in the
journal

Tested: Verified only one instance of kernel messages were
in the journal.

Resolves openbmc/openbmc#2720

Change-Id: I434f48159990e7b068103e5c11ac3c9431112199
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>