msm: mdss: synchronize recovery handler access

The recovery handler is used in the dsi event thread, and
the recovery handler variable was configured from a different
thread.  Earlier, there is no synchronization between the two
threads accessing the recovery handler, causing kernel panics.

Signed-off-by: Xiaoming Zhou <zhoux@codeaurora.org>
Signed-off-by: Shivaraj Shetty <shivaraj@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>