msm: mdss: Fix DSI event handler for dynamic FPS configuration

Commit 1c3fce18 introduced a bug which resulted in the dynamic
fps configuration function being called in response to the
command list kickoff event. This results in incorrect failure
logs getting printed whenever DSI operates in command mode.

Change-Id: I57359f624c2d6ddaa1a4c2fd7a5946ce9112ca16
Signed-off-by: Aravind Venkateswaran <aravindh@codeaurora.org>