Update version for v2.5.0-rc0 release

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/VERSION b/VERSION
index 9cf89c6..38f621b 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.4.50
+2.4.90