cxgb4: Fix offset when clearing filter byte counters

Pass the correct offset to clear the stale filter hit
bytes counter. Otherwise, the counter starts incrementing
from the stale information, instead of 0.

Fixes: 12b276fb ("cxgb4: add support to create hash filters")
Signed-off-by: Ganji Aravind <ganji.aravind@chelsio.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>