Quiet the SurfaceFlingerClient dequeueBuffer error.

This is a temporary WAR for the case where dequeueBuffer is called when
all the buffers owned by a SurfaceTexture are not available - either
they're the current texture buffer or the next one.  Currently, an error
is returned in that case, and this change just prevents that error from
being logged.  In the future this will be fixed to not return an error
in that case.

Bug: 3356050
Change-Id: Ic6cc304881a63ce134cfd0bcb4265e3e3fa94b6a