staging: octeon-usb: use __delay() instead of cvmx_wait()

Commit edf188be ("MIPS: Octeon: Remove usage of cvmx_wait()
everywhere.") deleted cvmx_wait() but forgot to update OCTEON USB
staging driver. Fix that to allow driver build.

Fixes: edf188be

 ("MIPS: Octeon: Remove usage of cvmx_wait() everywhere.")
Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Reviewed-by: James Hogan <jhogan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>