md: fix bug in raid10 recovery.

commit a53a6c85756339f82ff19e001e90cfba2d6299a8 upstream

Adding a spare to a raid10 doesn't cause recovery to start.
This is due to an silly type in
  commit 6c2fce2ef6b4821c21b5c42c7207cb9cf8c87eda
and so is a bug in 2.6.27 and .28-rc.

Thanks to Thomas Backlund for bisecting to find this.

Cc: Thomas Backlund <tmb@mandriva.org>
Cc: George Spelvin <linux@horizon.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>