octeontx2-af: cn10k: fix an array overflow in is_lmac_valid()

The value of "lmac_id" can be controlled by the user and if it is larger
then the number of bits in long then it reads outside the bitmap.
The highest valid value is less than MAX_LMAC_PER_CGX (4).

Fixes: 91c6945e

 ("octeontx2-af: cn10k: Add RPM MAC support")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>