drm/msm/dpu: simplify and unify dpu_encoder_get_intf and dpu_encoder_get_wb

Remove extra nestting level from the dpu_encoder_get_intf(), replacing it
with the explicit return in case the INTF_WB was passed to the function.

While we are at it, also change dpu_encoder_get_wb() to also use
explicit return rather than the goto.

Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/491189/
Link: https://lore.kernel.org/r/20220625003028.383259-1-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>