msm: mdss: fix incorrect fb_split reporting during ping-pong split

When ping-pong split mode is used, there is only 1 layer mixer is used.
Thus fb_split should be 0. However, current implementation incorrectly
reports fb_split which leads user-space to split layer into 2 pipes. But
in low tier chips number of pipes are less and this leads to display
boot-up failure. Fix this by sending lm_width as 0 when ping-pong split
is used.

Change-Id: Id7feb1a3fd1932e68bc910c7e7ecd3dcdf63cb5e
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>