Fix an issue of SPV generation for imageAtomicStore.

For GLSL function imageAtomicStore, it will be translated to
OpImageTexelPointer + OpAtomicStore. The result type of
OpImageTexelPointer must be the same as the sampled type of OpTypeImage.
On translation, the result type is mistakenly fetched from operand list
operands[2] while operands[2] corresponds to sampleNum whose type is
always uint. This leads to an error if the image type is iimageXXX that is
int image.

Test/spv.memoryScopeSemantics.comp

@@ -69,5 +69,6 @@ void main()
     atomicAdd(bufferu.x, 5u, gl_ScopeDevice, 0, gl_SemanticsVolatile);
 
     imageAtomicStore(imageMS, ivec2(0,0), 1, 4, gl_ScopeDevice, gl_StorageSemanticsBuffer, gl_SemanticsRelease);
+    imageAtomicStore(imagei, ivec2(0,0), -7, gl_ScopeDevice, gl_StorageSemanticsBuffer, gl_SemanticsRelease);
 }