clk: imx: clk-scu: fix clk enable state save and restore

The scu clk_ops only inplements prepare() and unprepare() callback.
Saving the clock state during suspend by checking clk_hw_is_enabled()
is not safe as it's possible that some device drivers may only
disable the clocks without unprepare. Then the state retention will not
work for such clocks.

Fixing it by checking clk_hw_is_prepared() which is more reasonable
and safe.

Fixes: d0409631 ("clk: imx: scu: add suspend/resume support")
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Tested-by: Carlos Song <carlos.song@nxp.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Link: https://lore.kernel.org/r/20241027-imx-clk-v1-v3-4-89152574d1d7@nxp.com


Signed-off-by: Abel Vesa <abel.vesa@linaro.org>