[PATCH] 9p: fix rename return code

9p doesn't handle renames between directories -- however, we were returning
EPERM instead of EXDEV when we detected this case.

Signed-off-by: Eric Van Hensbergren <ericvh@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>