In preparation to reworking IRQ indices, move irq_tbl access to
a separate helper.
Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/550931/
Link: https://lore.kernel.org/r/20230802100426.4184892-5-dmitry.baryshkov@linaro.org