release: Update patch level to 99 after the 2.5.0 release

Sets the patch level to 99 for the 2.6 development cycle.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/VERSION b/VERSION
index 956d85e..5faa288 100644
--- a/VERSION
+++ b/VERSION
@@ -1,5 +1,5 @@
 VERSION_MAJOR = 2
 VERSION_MINOR = 5
-PATCHLEVEL = 0
+PATCHLEVEL = 99
 VERSION_TWEAK = 0
 EXTRAVERSION =