[PATCH] uml ubd driver: allow using up to 16 UBD devices

With 256 minors and 16 minors used per each UBD device, we can allow the use
of up to 16 UBD devices per UML.

Also chnage parse_unit and leave to the caller (which already do it) the check
for excess numbers, since this is just supposed to do raw parsing.

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