fix to use command name when SETEX/PSETEX fail

when using SETEX/PSETEX and when their expire time is less than 0
their error message are the same.

```c
redis 127.0.0.1:6379> SETEX mykey -1 "Hello"
(error) ERR invalid expire time in SETEX
(5.60s)
redis 127.0.0.1:6379> PSETEX mykey -1 "Hello"
(error) ERR invalid expire time in SETEX
(3.69s)
```

so I changed to use their own names when PSETEX fails
```c
redis 127.0.0.1:6379> SETEX mykey -1 "Hello"
(error) ERR invalid expire time in SETEX
redis 127.0.0.1:6379> PSETEX mykey -1 "Hello"
(error) ERR invalid expire time in PSETEX
redis 127.0.0.1:6379> 
```