core: Set n_busses appropriately on failure to start binding

We were cleaning up the allocated memory but failing to reset the number
of allocated busses to zero. This makes it harder to correctly clean up
the MCTP context later in the lifecycle.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: I392ef6d6f7ffa7af7bb33d1aedfc4968f1749f7b
diff --git a/core.c b/core.c
index 6bcfd29..8a2b899 100644
--- a/core.c
+++ b/core.c
@@ -320,6 +320,7 @@
 			mctp_prerr("Failed to start binding: %d", rc);
 			__mctp_free(mctp->busses);
 			mctp->busses = NULL;
+			mctp->n_busses = 0;
 		}
 	}