Use erase_raw_partition for unknown named partitions

Change-Id: I84014a851ebdfb2c228cff43879580a761c22708
diff --git a/extendedcommands.c b/extendedcommands.c
index 36e696a..95a5f07 100644
--- a/extendedcommands.c
+++ b/extendedcommands.c
@@ -418,7 +418,7 @@
 
     // device may simply be a name, like "system"
     if (device[0] != '/')
-        return erase_partition(device, fs_type);
+        return erase_raw_partition(device);
 
     // if this is SDEXT:, don't worry about it if it does not exist.
     if (0 == strcmp(path, "/sd-ext"))