[SPIRV] Fix assert in getOrCreateBaseRegister for i32 -1 (#114630)

When trying to create a const inst from a 32 bit signed value, we don't
want to sign-extend it to 64 bits, as the resulting value won't actually
fit in an `i32` if it was negative.

This fixes crashes in the following two tests after the APInt
constructor asserts were enabled in #114539:
```
Failed Tests (2):
  LLVM :: CodeGen/SPIRV/transcoding/RelationalOperators.ll
  LLVM :: CodeGen/SPIRV/uitofp-with-bool.ll
```

llvm/lib/Target/SPIRV/SPIRVGlobalRegistry.cpp

@@ -400,7 +400,7 @@ Register SPIRVGlobalRegistry::getOrCreateBaseRegister(
   }
   assert(Type->getOpcode() == SPIRV::OpTypeInt);
   SPIRVType *SpvBaseType = getOrCreateSPIRVIntegerType(BitWidth, I, TII);
-  return getOrCreateConstInt(Val->getUniqueInteger().getSExtValue(), I,
+  return getOrCreateConstInt(Val->getUniqueInteger().getZExtValue(), I,
                              SpvBaseType, TII, ZeroAsNull);
 }