msm_fb: display: update var in display commit

Need the value of var in display commit to update the double buffers.
If not, double buffering doesn't work in minui (eg. recovery and off-charger
mode)

Change-Id: I1fba52243cc781f18742131759245911d32c9b18
Signed-off-by: Devin Kim <dojip.kim@lge.com>
Signed-off-by: Naseer Ahmed <naseer@codeaurora.org>