md: replace the RAID_AUTORUN ioctl with a direct function call

Instead of using a spcial RAID_AUTORUN ioctl that only exists for
non-modular builds and is only called from the early init code, just
call the actual function directly.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: NeilBrown <neilb@suse.de>
Acked-by: Song Liu <song@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>