Reset tags for UNOFFICIAL builds

Don't force a buildtype unless one is actually set. Anything without
a type is UNOFFICIAL

Change-Id: I38742485e580e21c51ee5e3f10467e7afbf247d9
diff --git a/config/common.mk b/config/common.mk
index 52e9086..6b3e317 100644
--- a/config/common.mk
+++ b/config/common.mk
@@ -131,16 +131,17 @@
     CM_BUILDTYPE := RELEASE
 endif
 
-ifdef CM_EXTRAVERSION
-    # Force build type to EXPERIMENTAL
-    CM_BUILDTYPE := EXPERIMENTAL
-    # Add leading dash to CM_EXTRAVERSION
-    CM_EXTRAVERSION := -$(CM_EXTRAVERSION)
-endif
-
-# If CM_BUILDTYPE is not defined, set to UNOFFICIAL
-ifndef CM_BUILDTYPE
+ifdef CM_BUILDTYPE
+    ifdef CM_EXTRAVERSION
+        # Force build type to EXPERIMENTAL
+        CM_BUILDTYPE := EXPERIMENTAL
+        # Add leading dash to CM_EXTRAVERSION
+        CM_EXTRAVERSION := -$(CM_EXTRAVERSION)
+    endif
+else
+    # If CM_BUILDTYPE is not defined, set to UNOFFICIAL
     CM_BUILDTYPE := UNOFFICIAL
+    CM_EXTRAVERSION :=
 endif
 
 ifdef CM_RELEASE