Return error code directly in allocateHelper()

libs/ui/GraphicBufferAllocator falsely maps error != NO_ERROR to
NO_MEMORY upon allocation failure. However, from the driver
implementation point of view, we need to distinguish unsupported
v.s. oom, which is quite natural if the error code is returned
directly.

Bug: b/189221081
Test: Presubmit
Change-Id: I75ce2d0d4c723c0d58ba8c27b9b68404be424ac8