i3c: dw: use parity8 helper instead of open coding it

The kernel has now a generic helper for getting parity with easier to
understand semantics. Make use of it.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/20250107090204.6593-4-wsa+renesas@sang-engineering.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>