.set_sysclk() is effectively unused here. No machine drivers use
jz4740-i2s; and JZ4740_I2S_CLKSRC_EXT is the only selectable clock
source with simple-card, but that is also the default source and
has a fixed frequency, so configuring it would be redundant.

simple-card ignores -ENOTSUPP error codes when setting the sysclock,
so any device trees that do set the sysclock for some reason should
still work.

It's still possible to configure the clock parent manually in the
device tree and control frequency using other simple-card options,
so at the end of the day there's no real loss in functionality.
Signed-off-by: Aidan MacDonald <aidanmacdonald.0x0@gmail.com>
Reviewed-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20221028103418.17578-4-aidanmacdonald.0x0@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>