fbdev : do not fail vsync ioctl when display in low power state

Do not fail MSMFB_OVERLAY_VSYNC_CTRL when display in
low power or ultra low power state. As it prevent HAL
from enabling vsync again during active state.

Change-Id: Ibd1939862cfb2fefa64db337ebc8c540e2b3d09e
Signed-off-by: Namit Solanki <nsolanki@codeaurora.org>
Signed-off-by: Sachin Bhayare <sachin.bhayare@codeaurora.org>