[PATCH] uml: hostfs: unuse ROOT_DEV

Minimal patch removing uses of ROOT_DEV; next patch unexports it.  I've
opposed this, but I've planned to reintroduce the functionality without using
ROOT_DEV.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>