release: bump version to Zephyr 2.2.1

Update version to 2.2.1

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
diff --git a/VERSION b/VERSION
index 7251c26..dfa8abe 100644
--- a/VERSION
+++ b/VERSION
@@ -1,5 +1,5 @@
 VERSION_MAJOR = 2
 VERSION_MINOR = 2
-PATCHLEVEL = 0
+PATCHLEVEL = 1
 VERSION_TWEAK = 0
 EXTRAVERSION =