libstagefright: Make it possible to skip OMX buffer reallocation

Some devices don't like the call to setParameter() at this point, so
skip this call if enough buffers are already allocated. This check
was present in KitKat but got removed when code to allocate extra-
buffers was introduced.

Change-Id: I9c1267c2a2a755bc16448a6049cb2e4aff0b65bb