build: fix some warnings

Fix a couple of warnings:

-Werror=unused-parameter

so we can use meson's warning_level=3 and -Werror without build
failures.

Change-Id: I14487a56727469f6bda1cabccce8241ac1acb149
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/presence/gpio_presence.cpp b/presence/gpio_presence.cpp
index 4326602..d2d2892 100644
--- a/presence/gpio_presence.cpp
+++ b/presence/gpio_presence.cpp
@@ -81,8 +81,7 @@
 }
 
 // Callback handler when there is an activity on the FD
-int Presence::processEvents(sd_event_source* es, int fd, uint32_t revents,
-                            void* userData)
+int Presence::processEvents(sd_event_source*, int, uint32_t, void* userData)
 {
     auto presence = static_cast<Presence*>(userData);