iio: adc: lpc18xx_adc: Reorder clk_get_rate() function call

clk_get_rate() is not guaranteed to work if called before
clk_prepare_enable().

Reorder clk_get_rate(), so it's called after clk_prepare_enable() and
after devm_add_action_or_reset() of lpc18xx_clk_disable().

Not that this is not a problem on this particular device, but it is
good to remove a case that might get copied elsewhere.

Suggested-by: Jonathan Cameron <jic23@kernel.org>
Acked-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: André Gustavo Nakagomi Lopez <andregnl@usp.br>
Link: https://lore.kernel.org/r/YXag5l4xBkGQH3tq@Andryuu.br


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>