mapper: Fix mapper environment generation bug

Fix a logic issue that results in an emitted mapper environment file
with interfaces like: rg.openbmc and yz.openbmc_project

Change-Id: I5ad30e45da08123b7611390855c04237ff5b60de
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/classes/phosphor-mapper.bbclass b/classes/phosphor-mapper.bbclass
index 26f369b..71d26ec 100644
--- a/classes/phosphor-mapper.bbclass
+++ b/classes/phosphor-mapper.bbclass
@@ -34,7 +34,7 @@
                 os.makedirs(parent)
             path = os.path.join(
                 parent,
-                '-'.join(p[1:].split(os.sep)))
+                '-'.join(p.split(os.sep)))
             with open(path, 'w+') as fd:
                 pass