[PATCH] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]

This makes CONFIG_USB_STORAGE depend on CONFIG_SCSI rather than selecting it,
as selecting it makes CONFIG_USB_STORAGE override the dependencies of SCSI,
causing it to turn on even if they aren't all met.

Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>