disp: msm: dp: fix DP controller bpc configuration when DSC is enabled

When DSC is enabled, dp controller uses the 8bpc data format to
transfer the data irrespective of the actual input bpc to DSC.

Change-Id: I817093e9726d013f0402bfdddfbccec59a900acc
Signed-off-by: Amine Najahi <anajahi@codeaurora.org>