Fix Cpu Conv3d gcc 8.3 build issues

Resolves: COMPMID-4986

Signed-off-by: Freddie Liardet <frederick.liardet@arm.com>
Change-Id: I54b682d377f3bcfc57fec54113debc5e8a1d75df
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/6745
Reviewed-by: Gunes Bayir <gunes.bayir@arm.com>
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
diff --git a/src/cpu/kernels/conv3d/neon/quantized.h b/src/cpu/kernels/conv3d/neon/quantized.h
index cdbc45e..a8165b4 100644
--- a/src/cpu/kernels/conv3d/neon/quantized.h
+++ b/src/cpu/kernels/conv3d/neon/quantized.h
@@ -171,7 +171,7 @@
                         {
                             const auto src_vec = wrapper::vloadq(in_ptr_mover);
                             //Load Cin weights
-                            for(unsigned int k = 0; k < num_elems_read_per_iteration; ++k, weights_ptr_mover += index_c_out_end)
+                            for(int k = 0; k < num_elems_read_per_iteration; ++k, weights_ptr_mover += index_c_out_end)
                             {
                                 w_vec = wrapper::vsetlane(*weights_ptr_mover, w_vec, k);
                             }