init: export name_to_dev_t and mark name argument as const

DM will switch its device lookup code to using name_to_dev_t() so it
must be exported.  Also, the @name argument should be marked const.

Signed-off-by: Dan Ehrenberg <dehrenberg@chromium.org>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --cc include/linux/mount.h
Simple merge

diff --cc init/do_mounts.c
Simple merge