msm: mdss: check for validity of ESD thread before scheduling it

Before scheduling the ESD thread during fb_event_callback and
updating the relevant data structures, check if ESD is valid
for that particular frame buffer. This avoids issues during
WFD connect use cases, where the dsi_status_data's mfd structure
gets corrupted with FB1 and leads to target crash during the next
ESD check due to invalid pointer dereferences.

Change-Id: Ia50a0b3c1ee74c4f574da6960a1b6d1707c3a89f
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>