Ensure the assert in IsEmbMaskOp is correct (#98306)

* Ensure the assert in IsEmbMaskOp is correct

* Have IsEmbMaskOp check, rather than assert, the node is a HWIntrinsic

Author: tannergooding

src/coreclr/jit/gentree.h

@@ -2244,13 +2244,12 @@ struct GenTree
 #if defined(TARGET_XARCH) && defined(FEATURE_HW_INTRINSICS)
     bool IsEmbMaskOp()
     {
-        bool result = (gtFlags & GTF_HW_EM_OP) != 0;
-        assert(!result || (gtOper == GT_HWINTRINSIC));
-        return result;
+        return OperIsHWIntrinsic() && ((gtFlags & GTF_HW_EM_OP) != 0);
     }
 
     void MakeEmbMaskOp()
     {
+        assert(OperIsHWIntrinsic());
         assert(!IsEmbMaskOp());
         gtFlags |= GTF_HW_EM_OP;
     }