Fix a typo

CMakeLists.txt

@@ -762,7 +762,7 @@ if(WIN32)
 
   IF(MSVC_TOOLSET_VERSION)
     SET(MSVC_PREFIX "vc${MSVC_TOOLSET_VERSION}")
-    SET(ASSIMP_MSVC_VERSION ${MCVS_PREFIX})
+    SET(ASSIMP_MSVC_VERSION ${MSVC_PREFIX})
   ELSE()
     IF(MSVC12)
       SET(ASSIMP_MSVC_VERSION "vc120")