msm_fb: display: add fput_light to frame buffer

Frame buffer's (fb0) ref_count need to be balanced. overlay_play()
increase fb0's ref_count (fget_light). This patch will decrease fb0's
ref_count by calling fput_light after commit.

Change-Id: I34ea738bf21d0858b7361ec8e289464a217a1231
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>