md/raid10: fix careless build error

build error introduced by commit b357f04a



That function doesn't get extra args until a later patch.  Bother.

Reported-by: Fengguang Wu <wfg@linux.intel.com>
Reported-by: Simon Kirby <sim@hostway.ca>
Reported-by: Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de>
Signed-off-by: NeilBrown <neilb@suse.de>