msm_fb: Correctly setup splash screen flag in MDP probe

The continuous splash screen flag was sometimes not correctly setup
during MDP probe causing corrupted grey screen on resets.

Crs-fixed: 389531
Change-Id: Id88d8a239ccfd1cbb5ce0f4f3db68756182f5ff9
Signed-off-by: Siddhartha Agrawal <agrawals@codeaurora.org>