drm/msm/dp: Fix platform_get_irq() check

drm/msm/dp: Fix platform_get_irq() check

The platform_get_irq() function returns negative error codes.  It never
returns zero.  Fix the check accordingly.

Fixes: 82c2a5751227 ("drm/msm/dp: tie dp_display_irq_handler() with dp driver")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/570755/
Link: https://lore.kernel.org/r/c12bb69b-d676-4345-9712-48aab48f2b48@moroto.mountain
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>