msm_fb: display: fix the underrun issue when playing interlaced videos

Interlaced videos require higher mdp clk rate and the current code
sets mdp clk to max and return. However mdp clk calculation may still
give a result higher than max mdp clk, for this case the result is
kept and used later to enable blt mode to avoid underrun.

Signed-off-by: Huaibin Yang <huaibiny@codeaurora.org>
(cherry picked from commit 5dcea9b4522d3bdc1a0fe38406881b264ce074b8)

Change-Id: I0dd27c5be093fe009b161618d0f32b402558a508
Signed-off-by: Gopal Goberu <ggober@codeaurora.org>