msm: mdss: initialize fb split values during fb probe

Initialize fb split left/right to 0 during fb probe, as there
might be cases where these variables are not updated at all.
Based on these variables the split_mode is set, which might
lead to wrong assumption if these holds garbage values.

CRs-fixed: 971626
Change-Id: Ic5d28ce4ab5792c1be4a71b00e6b50aba9083230
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>