ARM: shmobile: kzm9d: remove nfsroot settings from bootargs

NFS detail settings like "nfsroot=,rsize=4096,wsize=4096" are no longer needed

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>