usb-ohci: add missing memory barriers
usb-ohci: add missing memory barriers

* Start the control/bulk processing after ed is written
* Clear the content of control_head_ed and bulk_head_ed
  once done using them.

Signed-off-by: Nikunj A Dadhania <e2f4a5db9b4735182a88051d1e7a3599f9eac9db@linux.vnet.ibm.com>

mdroth/SLOF,stefanberger/SLOF-tpm,open-power-host-os/slof,qemu/SLOF,leilihh/SLOF,k0da/SLOF,mdroth/SLOF,stefanberger/SLOF-tpm,leilihh/SLOF,k0da/SLOF,aik/SLOF,qemu/SLOF,aik/SLOF,dgibson/SLOF,k0da/SLOF,aik/SLOF,open-power-host-os/slof,stefanberger/SLOF-tpm,k0da/SLOF,agraf/SLOF,dgibson/SLOF,mdroth/SLOF,agraf/SLOF,qemu/SLOF,agraf/SLOF,dgibson/SLOF,open-power-host-os/slof,mdroth/SLOF,open-power-host-os/slof,agraf/SLOF,dgibson/SLOF,leilihh/SLOF,leilihh/SLOF