Allow virtgpu_address_space_open to continue without CONTEXT_INIT

... to work with potentially older kernels which don't have
CONTEXT_INIT.

Bug: b/217188847
Test: boot Cuttlefish in aosp/master with 4.19 kernel
Change-Id: Ib8e6271da10f3f06511954653eedc936f68ae9c1
1 file changed