port: Make PORT_TYPES_MAX constant

Change-Id: I5f5b4a2d0a52ef12ac4e396f40002e8dec916cfb
Signed-off-by: Timo Wischer <twischer@de.adit-jv.com>

common/JackPortType.cpp

@@ -30,7 +30,7 @@ static const JackPortType* gPortTypes[] =
     &gMidiPortType,
 };
 
-jack_port_type_id_t PORT_TYPES_MAX = sizeof(gPortTypes) / sizeof(gPortTypes[0]);
+const jack_port_type_id_t PORT_TYPES_MAX = sizeof(gPortTypes) / sizeof(gPortTypes[0]);
 
 jack_port_type_id_t GetPortTypeId(const char* port_type)
 {

common/JackPortType.h

@@ -27,7 +27,7 @@ Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 namespace Jack
 {
 
-extern jack_port_type_id_t PORT_TYPES_MAX;
+extern const jack_port_type_id_t PORT_TYPES_MAX;
 
 struct JackPortType
 {