Followup to deepspeedai#7973 for deepspeedai#7971

The naming of q_mantisa_bits and mantisa_bits was swapped. The
invocation set:

```
q_mantisa_bits = mantisa
_mantisa_bits = CONST_Q_MANTISA_BITS
_exponent_bits = CONST_Q_EXPONENT_BITS
```

so correct them by swapping the names back.

I noticed that the code needs a thorough review because multiple places
look suspicious:
```
	// Why the default args? They seem to not even be matching (16 != 3+4+1)
          int total_q_bits = 16,
          int q_mantisa_bits = 3,
          int q_exponent_bits = 4>

	// Why recompute if there is a total_q_bits template?
    constexpr int quantized_bits = q_mantisa_bits + q_exponent_bits + 1;
    // Likely wrong: total_q_bits < mantisa_bits --> negative bits? Likely caused by wrong naming
    constexpr int q_exponent_bits = total_q_bits - mantisa_bits - 1;

    // should likey use a `q_` prefix not `_`
    constexpr uint16_t _mantisa_mask = (1 << q_mantisa_bits) - 1;
    constexpr uint16_t _exponent_mask = ((1 << q_exponent_bits) - 1) << q_mantisa_bits;
    constexpr uint16_t _sign_mask = 1U << (q_mantisa_bits + q_exponent_bits);
```

cc @Cursx

Signed-off-by: Alexander Grund <alexander.grund@tu-dresden.de>
Signed-off-by: ming.lee <ming.lee@inceptionai.ai>