[Bug] Config set maxmemory not return correct result

[hongliuliao]

the cmd "config set maxmemory 111" run the code like bebind:

freeMemoryIfNeeded may run failed , but it return OK

Reappear step:

• 1. fill some no ttl keys to redis , maxmemory-policy: volatile-lru
     
• 2. set maxmemory to 200000000, it return OK
• 3. we can see warning log like " WARNING: the new maxmemory value set via CONFIG SET is smaller than the current memory usage. This will result in keys eviction and/or inability to accept new write commands depending on the maxmemory-policy" , redis memory usage is not reduce
• 4. Because we not set key ttl , so freeMemoryIfNeeded will return C_ERR, i think we need return error for this case.