drm/msm/sde: Change error log to info when device suspend

Change error message to info log when crtc is not attached
after device suspend. This is to pass the display post
processing automation test of device suspend and resume.

Change-Id: I6aa1e499c9ac5d98f37d4fbf223ebc7c7c72b4ec
Signed-off-by: Xu Yang <yangxu@codeaurora.org>