SurfaceFlinger: mFbProducerSlot initailization

b/12487813

SurfaceFlinger crash is observed during simulation of
Secondary display

Note: change 14e8b01a
removed the initialization leading to the crash when
simulating secondary display.  Restore the initialization
to solve the problem.

Change-Id: Iae5845fb82735e01de5cc0dc582d13c27e3c614f
Signed-off-by: mayank parshar <mayankp@broadcom.com>
Signed-off-by: Pierre Couillaud <pierre@broadcom.com>