irqchip/ath79-cpu: Remove unused function

irqchip/ath79-cpu: Remove unused function

ath79_cpu_irq_init() was part of the legacy pre-OF code that got removed a
while back.

Remove it to get rid of a missing prototype warning, reported by the kernel test
robot.

[ tglx: Fix the subject prefix. Sigh ... ]

Fixes: 51fa4f8912c0 ("MIPS: ath79: drop legacy IRQ code")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260506085522.1210143-1-rosenp@gmail.com
Closes: https://lore.kernel.org/oe-kbuild-all/202412011509.kGQkDr1y-lkp@intel.com/