drm/msm/dp: Fix compile warnings

Fix the following compiler warning(s) from gcc 6.1.1 with -Werror enabled:

 drivers/gpu/drm/msm/sde_hdcp_2x.c:405:
   case label does not reduce to an integer constant
  case hdcp_min_enc_level_0:
 drivers/gpu/drm/msm/sde_hdcp_2x.c:406:
   case label does not reduce to an integer constant
  case hdcp_min_enc_level_1:
 drivers/gpu/drm/msm/sde_hdcp_2x.c:409:
   case label does not reduce to an integer constant
  case hdcp_min_enc_level_2:

Fixes: 10ffbfa2 ("drm/msm/dp: Snapshot of DP and supporting files")
Change-Id: Ic0dedbadd20c29ca0d053e3e258f173ba8cda714
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>