COMPMID-713: Address failures in OCLGrind for CLDirectConvolution

-Changes way of clamping in the kernel side.
-Fills padding with quantized values

Change-Id: I94d17c341fd637fbb24390722162b551b62d16cb
Reviewed-on: https://eu-gerrit-1.euhpc.arm.com/111114
Reviewed-by: Anthony Barbier <anthony.barbier@arm.com>
Tested-by: BSG Visual Compute Jenkins server to access repositories on http://mpd-gerrit.cambridge.arm.com <bsgcomp@arm.com>
diff --git a/tests/validation/fixtures/DirectConvolutionLayerFixture.h b/tests/validation/fixtures/DirectConvolutionLayerFixture.h
index 1ec4d31..b78f13a 100644
--- a/tests/validation/fixtures/DirectConvolutionLayerFixture.h
+++ b/tests/validation/fixtures/DirectConvolutionLayerFixture.h
@@ -73,7 +73,7 @@
         {
             case DataType::QASYMM8:
             {
-                std::uniform_int_distribution<uint8_t> distribution(0, 10);
+                std::uniform_int_distribution<uint8_t> distribution(0, 50);
                 library->fill(tensor, distribution, i);
                 break;
             }
@@ -86,7 +86,7 @@
             }
             case DataType::S32:
             {
-                std::uniform_int_distribution<int32_t> distribution(-1000, 1000);
+                std::uniform_int_distribution<int32_t> distribution(-5, 5);
                 library->fill(tensor, distribution, i);
                 break;
             }