libdvd: fix setting compiler when cross-compiling

Fix setting exact compiler when cross-compiling libdvd*
Otherwise it can result in problems when configure decides to use
one with different ABI

==
[..]/libdvdnav.a: member [..]/libdvdnav.a(dvdnav.o) in archive
is not an object
collect2: error: ld returned 1 exit status
CMakeFiles/wrap_libdvdnav.dir/build.make:63: recipe for target
'system/players/VideoPlayer/libdvdnav-arm.so' failed
==

project/cmake/modules/FindLibDvd.cmake

@@ -76,7 +76,7 @@ if(NOT WIN32)
     endforeach()
 
     set(DVDREAD_CFLAGS "${DVDREAD_CFLAGS} -I${CMAKE_BINARY_DIR}/${CORE_BUILD_DIR}/libdvd/include")
-    if(KODI_DEPENDSBUILD)
+    if(CMAKE_CROSSCOMPILING)
       set(EXTRA_FLAGS "CC=${CMAKE_C_COMPILER}")
     endif()