msm_fb: display: add fput_light to frame buffer

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

Change-Id: I352da1fce99b344c059f615a6fe88cc6e7387d89
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
Signed-off-by: Naseer Ahmed <naseer@codeaurora.org>
Signed-off-by: Iliyan Malchev <malchev@google.com>