mfd: max8925: Remove the unused function irq_to_max8925()

The function irq_to_max8925() is defined in the max8925-core.c
file, but not called elsewhere, so remove this unused function.

  drivers/mfd/max8925-core.c:472:40: warning: unused function 'irq_to_max8925'.

Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=3561


Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20221227081805.54185-1-jiapeng.chong@linux.alibaba.com