Update error in XML schema.

Signed-off-by: Keith Rothman <537074+litghost@users.noreply.github.com>

fpga_architecture.xsd

diff --git a/fpga_architecture.xsd b/fpga_architecture.xsd
index 70018d8..0f844ea 100644
--- a/fpga_architecture.xsd
+++ b/fpga_architecture.xsd
@@ -48,7 +48,7 @@
 

   <xs:complexType name="port_list">

     <xs:sequence>

-      <xs:element name="port" type="port" maxOccurs="unbounded" />

+      <xs:element name="port" type="port" minOccurs="0" maxOccurs="unbounded" />

     </xs:sequence>

   </xs:complexType>