[SPIR-V] OpStore Pointer error when using asuint (splitdouble version)

**Description**
Invalid SPIRV produced when using asuint (splitdouble version)

**Steps to Reproduce**
https://godbolt.org/z/8bPnE1sf8

**Actual Behavior**
```
fatal error: generated SPIR-V is invalid: OpStore Pointer <id> '23[%23]' is not a logical pointer.
 OpStore %23 %36
```

**Environment**
- DXC version 1.8.2502
- Host Operating System N/A
