ntb: no sleep in ntb_async_tx_submit

Do not sleep in ntb_async_tx_submit, which could deadlock.
This reverts commit "8c874cc1"

Fixes: 8c874cc1 ("NTB: Address out of DMA descriptor issue with NTB")
Reported-by: Jia-Ju Bai <baijiaju1990@163.com>
Signed-off-by: Allen Hubbe <Allen.Hubbe@dell.com>
Acked-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>