Propagate error code from prepareModel

Prior to this CL, when a driver returned an error when preparing a
model, the runtime would change the error code to OP_FAILED. Instead,
this CL propagates the error returned from preparing the model as-is.

Fixes: 189160433
Test: mma
Test: NeuralNetworksTest_static
Change-Id: Ic69eb7982aebe68b294e72fc688355934ad58c8f