HWComposer: Fix an fd leak on boot with HDMI

When the device is booting with an attached external display, every
frame leaks a file descriptor until the display manager enables the
external display, resulting in hundreds of leaked descriptors. This
plugs the leak.

Change-Id: Ib7e2af3638dab28c2ed04c02ddf9c485edf2bb9d
1 file changed