mboxd: Update service file to require device dependencies

In line with Andrew Geissler's proposal for managing unit/target
failures[1], update mboxd.service to require the device dependencies.

Tested with a Zaius image under QEMU (-M romulus-bmc).

[1] https://lists.ozlabs.org/pipermail/openbmc/2017-February/006370.html

Change-Id: I1cc6c64871917ab0d51917833909a1795b6662f2
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/common/recipes-phosphor/mboxd/mboxd/mboxd.service b/common/recipes-phosphor/mboxd/mboxd/mboxd.service
index 0d37a48..dda2532 100644
--- a/common/recipes-phosphor/mboxd/mboxd/mboxd.service
+++ b/common/recipes-phosphor/mboxd/mboxd/mboxd.service
@@ -1,8 +1,8 @@
 [Unit]
 Description=Phosphor MBOX Daemon
-Wants=dev-aspeed\x2dlpc\x2dctrl.device
+BindsTo=dev-aspeed\x2dlpc\x2dctrl.device
 After=dev-aspeed\x2dlpc\x2dctrl.device
-Wants=dev-aspeed\x2dmbox.device
+BindsTo=dev-aspeed\x2dmbox.device
 After=dev-aspeed\x2dmbox.device