net: atlantic: use U32_MAX in aq_hw_utils.c

This patch replaces magic constant ~0U usage with U32_MAX in aq_hw_utils.c

Signed-off-by: Mark Starovoytov <mstarovoitov@marvell.com>
Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>