[PATCH] remove EXPORT_SYMBOL for root_dev

Remove ROOT_DEV after unexporting it in the previous patch, as requested time
ago by Christoph Hellwig.

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>