Always create separate dynamic vertex buffer for compute.

src/bgfx_p.h

@@ -2625,7 +2625,7 @@ namespace bgfx
 			uint32_t size = bx::strideAlign16(_num*_decl.m_stride, _decl.m_stride);
 
 			uint64_t ptr = 0;
-			if (0 != (_flags & BGFX_BUFFER_COMPUTE_WRITE) )
+			if (0 != (_flags & BGFX_BUFFER_COMPUTE_READ_WRITE) )
 			{
 				VertexBufferHandle vertexBufferHandle = { m_vertexBufferHandle.alloc() };
 				if (!isValid(vertexBufferHandle) )