exynos/gralloc3/src/mali_gralloc_debug.cpp: use Strings8/16 empty()

Only changed in one file to fix compilation errors.

Change-Id: Id9763428249a74326a38f005b9cc760adbe039f1
diff --git a/gralloc3/src/mali_gralloc_debug.cpp b/gralloc3/src/mali_gralloc_debug.cpp
index 39a2b66..975726a 100644
--- a/gralloc3/src/mali_gralloc_debug.cpp
+++ b/gralloc3/src/mali_gralloc_debug.cpp
@@ -120,7 +120,7 @@
 
 	if (NULL == outBuffer)
 	{
-		if (!dumpStrings.isEmpty())
+		if (!dumpStrings.empty())
 		{
 			dumpStrings.clear();
 		}
@@ -129,7 +129,7 @@
 	}
 	else
 	{
-		if (dumpStrings.isEmpty())
+		if (dumpStrings.empty())
 		{
 			*outSize = 0;
 		}