tools/testing/selftests/ipc/msgque.c: handle msgget failure return correctly

A failed msgget causes the test to return an uninitialised value in ret.
Assign ret to -errno on error exit.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Davidlohr Bueso <davidlohr@hp.com>
Cc: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>