cxgb4: remove unneeded if-null-free check

Eliminate the following coccicheck warning:

drivers/net/ethernet/chelsio/cxgb4/cxgb4_tc_u32.c:529:3-9: WARNING:
 NULL check before some freeing functions is not needed.
drivers/net/ethernet/chelsio/cxgb4/cxgb4_tc_u32.c:533:2-8: WARNING:
 NULL check before some freeing functions is not needed.
drivers/net/ethernet/chelsio/cxgb4/cxgb4_cudbg.c:161:2-7: WARNING:
 NULL check before some freeing functions is not needed.
drivers/net/ethernet/chelsio/cxgb4/clip_tbl.c:327:3-9: WARNING:
 NULL check before some freeing functions is not needed.

Signed-off-by: Qiheng Lin <linqiheng@huawei.com>
Link: https://lore.kernel.org/r/20210409115339.4598-1-linqiheng@huawei.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>