irqchip: renesas-rzg2l: Fix logic to clear TINT interrupt source

The logic to clear the TINT interrupt source in rzg2l_irqc_irq_disable()
is wrong as the mask is correct only for LSB on the TSSR register.
This issue is found when testing with two TINT interrupt sources. So fix
the logic for all TINTs by using the macro TSSEL_SHIFT() to multiply
tssr_offset with 8.

Fixes: 3fed0955

 ("irqchip: Add RZ/G2L IA55 Interrupt Controller driver")
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Tested-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230918122411.237635-2-biju.das.jz@bp.renesas.com