net: dpaa2-eth: export the CH#<index> in the 'ch_stats' debug file

Just give out an index for each channel that we export into the debug
file in the form of CH#<index>. This is purely to help corelate each
channel information from one debugfs file to another one.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>