drm/msm/dpu: fix error handling around dpu_hw_vbif_init

drm/msm/dpu: fix error handling around dpu_hw_vbif_init

Using IS_ERR_OR_NULL() together with PTR_ERR() is a typical mistake. If
the value is NULL, then the function will return 0 instead of a proper
return code. Moreover dpu_hw_vbif_init() function can not return NULL.
So, replace corresponding IS_ERR_OR_NULL() call with IS_ERR().

Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/489570/
Link: https://lore.kernel.org/r/20220615125703.24647-2-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>