drm:msm:sde: avoid CWB connector in determining active crtc

CWB connector is tied to primary crtc along with primary connector.
Avoid using CWB connector power state in determining active crtc,
as it is already done via primary connector.

Change-Id: I35ec95349790990c49b9a63afd6e0f55d23b4887
Signed-off-by: Kalyan Thota <kalyant@codeaurora.org>