Reference rockchip I2S controller TRM, modify some registers' property
I2S_FIFOLR: read / write, but not volatile, not precious
I2S_INTSR: read / write
I2S_CLR: volatile, register value will be cleared by read

Test on RK3288 with max98090.
Signed-off-by: Jianqun Xu <jay.xu@rock-chips.com>
Signed-off-by: Mark Brown <broonie@kernel.org>