Fix typo in local variable name in time_stop

This didn't break functionality but it would use a global instead
of a local variable so nested calls to time_* might have issues.

Change-Id: If61ef07c4ce15f1a356975a0b0611fdf5e49109a
diff --git a/functions-common b/functions-common
index 9973d8f..3fdd71b 100644
--- a/functions-common
+++ b/functions-common
@@ -2371,7 +2371,7 @@
 function time_stop {
     local name
     local end_time
-    local elpased_time
+    local elapsed_time
     local total
     local start_time