FST: Use -EINVAL instead of EINVAL as return value

This is more consistent with other error cases.

Signed-off-by: Jouni Malinen <j@w1.fi>

hostapd/ctrl_iface.c

@@ -2586,7 +2586,7 @@ hostapd_global_ctrl_iface_fst_attach(struct hapd_interfaces *interfaces,
 		}
 	}
 
-	return EINVAL;
+	return -EINVAL;
 }
 
 
@@ -2608,7 +2608,7 @@ hostapd_global_ctrl_iface_fst_detach(struct hapd_interfaces *interfaces,
 		}
 	}
 
-	return EINVAL;
+	return -EINVAL;
 }
 
 #endif /* CONFIG_FST */