drm/msm/dpu: make the irq table size static

The size of the irq table is static, it has MDP_INTR_MAX * 32 interrupt
entries. Provide the fixed length and drop struct_size() statement.

Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/550927/
Link: https://lore.kernel.org/r/20230802100426.4184892-6-dmitry.baryshkov@linaro.org