disp: msm: dp: return early if all streams are disabled

Return early if the active streams are not present. Clean function
doesn't take into account the count of active stream which is being
changed during disable and link clk is turned off before that.
Adding active stream check in pre_off will ensures atleast one
stream is on and link clk is not turned off.

Change-Id: I6abf4b14ae4f99161eed3d5300b1961a1983977d
Signed-off-by: Rajat Gupta <rajatgu@codeaurora.org>