cxgb4: fix the panic caused by non smac rewrite

cxgb4: fix the panic caused by non smac rewrite

[ Upstream commit bff453921ae105a8dbbad0ed7dd5f5ce424536e7 ]

SMT entry is allocated only when loopback Source MAC
rewriting is requested. Accessing SMT entry for non
smac rewrite cases results in kernel panic.

Fix the panic caused by non smac rewrite

Fixes: 937d84205884 ("cxgb4: set up filter action after rewrites")
Signed-off-by: Raju Rangoju <rajur@chelsio.com>
Link: https://lore.kernel.org/r/20201118143213.13319-1-rajur@chelsio.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>