rtc: emul_rtc: Make emul_rtc_probe() static

emul_rtc_probe() is not called from anywhere else that's why make it
static. Issue is reported by build with W=1.

Signed-off-by: Michal Simek <michal.simek@amd.com>
diff --git a/drivers/rtc/emul_rtc.c b/drivers/rtc/emul_rtc.c
index 97a8d9b..6817daa 100644
--- a/drivers/rtc/emul_rtc.c
+++ b/drivers/rtc/emul_rtc.c
@@ -58,7 +58,7 @@
 	return 0;
 }
 
-int emul_rtc_probe(struct udevice *dev)
+static int emul_rtc_probe(struct udevice *dev)
 {
 	struct emul_rtc *priv = dev_get_priv(dev);
 	const char *epoch_str;