fsl/fman: fix unreachable code

The parameter 'priority' is incorrectly forced to zero which ultimately
induces logically dead code in the subsequent lines.

Fixes: 57ba4c9b

 ("fsl/fman: Add FMan MAC support")
Signed-off-by: Florinel Iordache <florinel.iordache@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>