stmmac: fix valid numbers of unicast filter entries

Synopsys DWC Ethernet MAC can be configured to have 1..32, 64, or
128 unicast filter entries. (Table 7-8 MAC Address Registers from
databook) Fix dwmac1000_validate_ucast_entries() to accept values
between 1 and 32 in addition.

Signed-off-by: Jongsung Kim <neidhard.kim@lge.com>
Signed-off-by: David S. Miller <davem@davemloft.net>