octeontx2-af: Fix some memory leaks in the error handling path of 'cgx_lmac_init()'

Memory allocated before 'lmac' is stored in 'cgx->lmac_idmap[]' must be
freed explicitly. Otherwise, in case of error, it will leak.

Rename the 'err_irq' label to better describe what is done at this place in
the error handling path.

Fixes: 6f14078e

 ("octeontx2-af: DMAC filter support in MAC block")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>