drivers: net: xgene: optimizing the code

this patch does the following:
1 .  remove unnecessary if, else condition
2 .  reduce one variable
3 .  change the return type of 2 functions to void as there return values
turn out to be 0 always after above changes

Signed-off-by: Saurabh Sengar <saurabh.truth@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>