disp: msm: sde: Init LTM phase init_h with single pipe value

Initialize LTM phase init_h values with single pipe configuration
value for both LTM blocks, so in dual panel use case, the correct
init_h values will be programed for LTM_0 and LTM_1.
As for dual pipe merge configuration, init_h value for LTM_1 will
be overwrite with the correct configuration if merge_en is set.

Change-Id: I8719b217cf7e5677e23c17b3c3f62f4ee23f43e9
Signed-off-by: Yuchao Ma <yuchaom@codeaurora.org>