mtd: rawnand: denali: Use the devm_clk_get_enabled() helper function

The devm_clk_get_enabled() helper:
  - calls devm_clk_get()
  - calls clk_prepare_enable() and registers what is needed in order to
    call clk_disable_unprepare() when needed, as a managed resource.

This simplifies the code.

Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20240826080408.2522978-1-ruanjinjie@huawei.com