ARM: shmobile: r8a7778: remove old style audio clock

Current sound driver moves to new style clock,
but is keeping compatiblity at this point.
Move to new style on r8a7778

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