Add channel-gen.cpp to compilation units

The commit c01edf283dca792d1eecedd5c03b69b7eebb6f23 in
phosphor-host-ipmid had introduced a breaking change. This
commit would fix that.

Change-Id: Id3aa18bcc3b7f054b8c659916896de146064d8bb
Signed-off-by: Tom Joseph <tomjoseph@in.ibm.com>
diff --git a/.gitignore b/.gitignore
index 7a36e8c..8e4dc30 100644
--- a/.gitignore
+++ b/.gitignore
@@ -63,3 +63,4 @@
 /inventory-sensor-gen.cpp
 /fru-read-gen.cpp
 /app/*.lo
+/channel-gen.cpp