gralloc: layercount validation check

layercount value should not be zero.

Change-Id: I439ca4f1655a4c892b4bdf02fc786c7e2838e816
diff --git a/gralloc/QtiMapper.cpp b/gralloc/QtiMapper.cpp
index 3848878..14c788e 100644
--- a/gralloc/QtiMapper.cpp
+++ b/gralloc/QtiMapper.cpp
@@ -52,7 +52,7 @@
 
 bool QtiMapper::ValidDescriptor(const BufferDescriptorInfo_2_1 &bd) {
   if (bd.width == 0 || bd.height == 0 || (static_cast<int32_t>(bd.format) <= 0) ||
-      bd.layerCount != 1) {
+      bd.layerCount <= 0) {
     return false;
   }