[MLIR, test] Fix use of undef FileCheck var

MLIR test Dialect/Linalg/tile-indexed-generic.mlir has a CHECK-NOT
directive referring to a variable only defined in a CHECK directive with
a different prefix, and thus undefined in the CHECK-NOT.

This commit removes the variable reference altogether to error on any
content it might have.

Reviewed By: pifon2a

Differential Revision: https://reviews.llvm.org/D99956

Author: Thomas Preud'homme

mlir/test/Dialect/Linalg/tile-indexed-generic.mlir

@@ -42,7 +42,7 @@ func @indexed_generic_vector(%operand: memref<50xf32>, %result: memref<50xf32>)
 // TILE-25n0:     %[[OUT:.*]] = addf %[[IN]], %[[NEW_I_FLOAT]] : f32
 
 // TILE-0n25-LABEL: func @indexed_generic_vector
-// TILE-0n25-NOT: scf.for %[[J:.*]] = {{.*}} step %[[C25]]
+// TILE-0n25-NOT: scf.for %[[J:.*]] = {{.*}} step %
 // TILE-0n25: linalg.indexed_generic
 
 #combined_indices_trait = {