regmap-irq: Remove unused mask_invert flag

mask_invert is deprecated and no longer used; it can now be removed.

Signed-off-by: Aidan MacDonald <aidanmacdonald.0x0@gmail.com>
Link: https://lore.kernel.org/r/20230216223200.150679-2-aidanmacdonald.0x0@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>