msm: mdss: fix mdp clock calculations for rotator

MDP clock requirement for rotator depends solely on source dimensions,
rot_clk = (src_w * src_h * fps). Fix current calculations where MDP clock
rate is incorrectly calculated as rot_clk = (dst_h * dst_h *fps). New
calculations are valid even when down-scale is done along with rotation.

Change-Id: I30d98b7a62beeb3a559a9c5f26de43c014fd25fd
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>