goldfish: pipe: ANDROID: mark local functions static

goldfish_dma_ioctl_getoff and goldfish_dma_ioctl_create_region
are not used outside of goldfish_pipe_v2.c - mark them
static.
Bug: 72717639
Bug: 66884503
Signed-off-by: Roman Kiryanov <rkir@google.com>
Change-Id: Id4fe524cc4db9d36b0c794ad9f34356f396153b4