[SCSI] fix CONFIG_SCSI_WAIT_SCAN=m

CONFIG_MODULES=y
CONFIG_SCSI=y
CONFIG_SCSI_SCAN_ASYNC=y
CONFIG_SCSI_WAIT_SCAN=m

2.6.21-rc5-mm2 VFS panics unable to find my root on /dev/sda2, but boots
okay if I change drivers/scsi/Kconfig to "default y" instead of "default m"
for SCSI_WAIT_SCAN.

Make sure there's a late_initcall to scsi_complete_async_scans when it's
built in, so a monolithic SCSI_SCAN_ASYNC kernel can rely on the scans
being completed before trying to mount root, even if they're slow.

[akpm@linux-foundation.org: build fixes]
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Acked-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>