ARM: shmobile: sh73a0: div4 clocks must check the kick bit before changing rate

According to the datasheet, it is not allowed to change div4 clock rates
if an earlier rate change operation is still in progress, as indicated by
a set kick bit.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski+renesas@gmail.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>