clk: mdss: fix pll 1 leakage issue by calling power down sequence

To completely shutdown pll 1, power down sequence has to be
called. This is different from the old sequence where disable pll
sequence acturally turn off pll.

Change-Id: Ia8b9adb8f78241e34420c0966c3c25b7684b1262
Signed-off-by: Huaibin Yang <huaibiny@codeaurora.org>