msm: mdss: Remove additional clk refcnts in dual-dsi

When dual-dsi panel is attached to a device, both DSI controllers
are registered to mdss. But only one registration done notification
needs to be sent. Currently two notifications are sent and it leads
to an additional refcnt on mdp clocks which in turn prevents proper
suspend. Fix this by sending notification only once.

Change-Id: I29e3c92e9ab0cccd9314cc5428b4accc31b0d0d9
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>