VR: Fix OVR_VERSION macro.

Was previously supplying (major,minor,build) when it is
actuall (product,major,minor).

For example, the 0.5.0 SDK has the following:
```
 #define OVR_PRODUCT_VERSION 0
 #define OVR_MAJOR_VERSION   5
 #define OVR_MINOR_VERSION   0
 #define OVR_PATCH_VERSION   1
 #define OVR_BUILD_NUMBER    0
```

src/ovr.h

@@ -13,7 +13,7 @@
 #	include <OVR_Version.h>
 
 #	define OVR_VERSION_(_a, _b, _c) (_a * 10000 + _b * 100 + _c)
-#	define OVR_VERSION     OVR_VERSION_(OVR_MAJOR_VERSION, OVR_MINOR_VERSION, OVR_BUILD_VERSION)
+#	define OVR_VERSION     OVR_VERSION_(OVR_PRODUCT_VERSION, OVR_MAJOR_VERSION, OVR_MINOR_VERSION)
 #	define OVR_VERSION_042 OVR_VERSION_(0, 4, 2)
 #	define OVR_VERSION_043 OVR_VERSION_(0, 4, 3)
 #	define OVR_VERSION_044 OVR_VERSION_(0, 4, 4)