In a case documented as

  We should never be called with any of these states

BUG() in a case that would later result in a NULL pointer dereference.
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>