Fix mismatched signedness for a compare in subzero

Clang 9 escalates a warning about an unsigned integer being compared
against a signed integer into an error.

Fixed by making an integer literal be unsigned.

Bug: b/152777669
Change-Id: I38c61ac0837f756c73b8664f7774719a94353fac
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/51530
Tested-by: Sean Risser <srisser@google.com>
Commit-Queue: Sean Risser <srisser@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
diff --git a/third_party/subzero/src/IceUtils.h b/third_party/subzero/src/IceUtils.h
index 2c7c62b..e600cf1 100644
--- a/third_party/subzero/src/IceUtils.h
+++ b/third_party/subzero/src/IceUtils.h
@@ -134,7 +134,7 @@
   // Don't call reserve() if Size==0.
   if (Size > 0) {
     uint32_t Mask;
-    if (Size <= (1 << ChunkSizeBits)) {
+    if (Size <= (1u << ChunkSizeBits)) {
       // For smaller sizes, reserve the smallest power of 2 greater than or
       // equal to Size.
       Mask =