Fix returning an opaque handle for eglGetCurrentDisplay().

Change-Id: If7524c5245951ed87bcb8caacda2264db0875dad
Reviewed-on: https://swiftshader-review.googlesource.com/4554
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>