drm/msm/dpu: Fix error return code in dpu_mdss_init()

drm/msm/dpu: Fix error return code in dpu_mdss_init()

The error code returned by platform_get_irq() is stored in 'irq', it's
forgotten to be copied to 'ret' before being returned. As a result, the
value 0 of 'ret' is returned incorrectly.

After the above fix is completed, initializing the local variable 'ret'
to 0 is no longer needed, remove it.

In addition, when dpu_mdss_init() is successfully returned, the value of
'ret' is always 0. Therefore, replace "return ret" with "return 0" to make
the code clearer.

Fixes: 070e64dc1bbc ("drm/msm/dpu: Convert to a chained irq chip")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Link: https://lore.kernel.org/r/20210510063805.3262-2-thunder.leizhen@huawei.com
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>