Daniel Swarbrick reports the following go vet warning after CL 50550:

  .../dev_linux.go:38: (major & 0xfffff000) (32 bits) too small for shift of 32

Fix it by converting major and minor to uint64 before the bitwise-and.

Change-Id: If37540be81f2c78a58fd5e5dcce7b770ce7b8afe
Reviewed-on: https://go-review.googlesource.com/63090Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>