irqchip/renesas-rzg2l: Rename rzg2l_irq_eoi()

Rename rzg2l_irq_eoi()->rzg2l_clear_irq_int() and simplify the code by
removing redundant priv local variable.

Suggested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>