amd-xgbe: Fix debug output of max channel counts

A debug output print statement uses the wrong variable to output the
maximum Rx channel count (cut and paste error, basically).  Fix the
statement to use the proper variable.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>