leds: leds-mt6323: Open code and drop MT6323_CAL_HW_DUTY macro

There is only one instance of using this macro and it's anyway not
simplifying the flow, or increasing the readability of this driver.

Drop this macro by open coding it in mt6323_led_set_blink().

No functional changes.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230601110813.2373764-7-angelogioacchino.delregno@collabora.com