drm/msm/dpu: remove unused refcount for encoder_phys_wb

drm/msm/dpu: remove unused refcount for encoder_phys_wb

Remove the unused local variable refcount for encoder_phys_wb
as the one part of wb_enc is used directly.

changes in v2:
	- remove usage of ret variable also
	- remove the if (ret) code as it was dead-code anyway

Fixes: d7d0e73f7de3 ("drm/msm/dpu: introduce the dpu_encoder_phys_* for writeback")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/483919/
Link: https://lore.kernel.org/r/1651169759-29760-1-git-send-email-quic_abhinavk@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>