fbdev: msm: check for target supports dest scaler

user space can send commit message with dest scaler structure populated,
this would cause null pointer access, if dest scaler is not initialized,
this change validate if target supports dest scaler.

Change-Id: I37516f4704a013d4628688930783d6e7ab93277f
Signed-off-by: Raghavendra Ambadas <rambad@codeaurora.org>