leds: leds-mt6323: Drop MT6323_ prefix from macros and defines

This renames all definitions and macros to drop the MT6323_ prefix,
since it is now possible to easily add support to more PMICs in
this driver.
While at it, also fix related formatting where possible.

This commit brings 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/20230601110813.2373764-6-angelogioacchino.delregno@collabora.com