mfd: sec: Don't compare against NULL / 0 for errors, use !

Follow general style and use if (!arg) instead of comparing against
NULL.

While at it, drop a useless init in sec-irq.c.

Signed-off-by: André Draszik <andre.draszik@linaro.org>
Link: https://lore.kernel.org/r/20250409-s2mpg10-v4-19-d66d5f39b6bf@linaro.org


Signed-off-by: Lee Jones <lee@kernel.org>