Move definition of vhloOperands right before it is used (#1920)

This makes the code a bit more readable. On my first read I was puzzled
as to why this getter was being called.

stablehlo/transforms/StablehloLegalizeToVhlo.cpp

@@ -792,10 +792,6 @@ class StablehloToVhloOpConverter : public OpConversionPattern<StablehloOpTy> {
       return failure();
     }
 
-    // These operands have already been converted to VHLO by
-    // the dialect conversion infrastructure.
-    ValueRange vhloOperands = adaptor.getOperands();
-
     // Convert StableHLO attributes to VHLO equivalents.
     // There are two paths:
     //   1) Generic path where default logic applies, and there is a 1:1
@@ -821,6 +817,10 @@ class StablehloToVhloOpConverter : public OpConversionPattern<StablehloOpTy> {
       }
     }
 
+    // These operands have already been converted to VHLO by
+    // the dialect conversion infrastructure.
+    ValueRange vhloOperands = adaptor.getOperands();
+
     // Convert the StableHLO operation to a VHLO equivalent.
     // This can almost be done in a generic fashion, except for
     // stablehlo.case that uses a variadic number of regions which means an