icd:Reduce offset alignment limits

Buffer min offset alignments were set to the max value. Reduce them to
16 to simplify testing of offsets that are a multiple of the min
alignment.
diff --git a/scripts/mock_icd_generator.py b/scripts/mock_icd_generator.py
index 899a75b..c0757e2 100644
--- a/scripts/mock_icd_generator.py
+++ b/scripts/mock_icd_generator.py
@@ -133,9 +133,9 @@
     limits->viewportBoundsRange[1] = 8191;
     limits->viewportSubPixelBits = 0;
     limits->minMemoryMapAlignment = 64;
-    limits->minTexelBufferOffsetAlignment = 256;
-    limits->minUniformBufferOffsetAlignment = 256;
-    limits->minStorageBufferOffsetAlignment = 256;
+    limits->minTexelBufferOffsetAlignment = 16;
+    limits->minUniformBufferOffsetAlignment = 16;
+    limits->minStorageBufferOffsetAlignment = 16;
     limits->minTexelOffset = -8;
     limits->maxTexelOffset = 7;
     limits->minTexelGatherOffset = -8;