[PATCH] knfsd: nfsd4: fix setclientid_confirm error return

NFS4_INVAL is not a valid error for setclientid_confirm, and INUSE is the more
logical error here anyway.

From: Fred Isaman
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>