goldfish: pipe: ANDROID: rename global variables

We don't need an array of 1 for pipe_dev and
use better names to distinguish between
goldfish_pipe_dev and miscdevice.

Bug: 72717639
Bug: 66884503
Change-Id: Iab040c158745f034ca8e9569fd49c84933b1c4ba
Signed-off-by: Roman Kiryanov <rkir@google.com>