Fix GEMMLowp output stage validation crash when input's first dimension == 1

- Change vectors' fixed length of 4 in gemmlowp_output_stage_quantize_down_float with its kernel's adjusted vec_size

Resolve COMPMID-4355

Signed-off-by: Giorgio Arena <giorgio.arena@arm.com>
Change-Id: I371ecf114356fb6a8d18c5c3727f09ae247484bd
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/5631
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Michele Di Giorgio <michele.digiorgio@arm.com>
Reviewed-by: Georgios Pinitas <georgios.pinitas@arm.com>
Tested-by: Arm Jenkins <bsgcomp@arm.com>
diff --git a/tests/datasets/ShapeDatasets.h b/tests/datasets/ShapeDatasets.h
index 558b37a..c2b4cd7 100644
--- a/tests/datasets/ShapeDatasets.h
+++ b/tests/datasets/ShapeDatasets.h
@@ -165,7 +165,7 @@
         : ShapeDataset("Shape",
     {
         // Batch size 1
-        TensorShape{ 9U, 9U },
+        TensorShape{ 1U, 9U },
                      TensorShape{ 27U, 13U, 2U },
     })
     {