net: yellowfin parenthesis fix

The code is under unused #ifdef NO_TXSTATS branch but its better to have it
fixed.

Signed-off-by: Mariusz Kozlowski <m.kozlowski@tuxland.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>