net: zynq_gem: Modify the nwcfg bit definitions

Modify the nwcfg bit definitions to have 32-bit
by removing the extra nibble.

Signed-off-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>