gve: Implement settime64 with -EOPNOTSUPP

ptp_clock_settime() assumes every ptp_clock has implemented settime64().
Stub it with -EOPNOTSUPP to prevent a NULL dereference.

Fixes: acd1638 ("gve: Add initial PTP device support")
Reported-by: syzbot+a546141ca6d53b90aba3@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=a546141ca6d53b90aba3
Signed-off-by: Tim Hostetler <thostet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Signed-off-by: Joshua Washington <joshwash@google.com>
Link: https://patch.msgid.link/20251029184555.3852952-3-joshwash@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: tdh911

drivers/net/ethernet/google/gve/gve_ptp.c

@@ -33,6 +33,12 @@ static int gve_ptp_gettimex64(struct ptp_clock_info *info,
 	return -EOPNOTSUPP;
 }
 
+static int gve_ptp_settime64(struct ptp_clock_info *info,
+			     const struct timespec64 *ts)
+{
+	return -EOPNOTSUPP;
+}
+
 static long gve_ptp_do_aux_work(struct ptp_clock_info *info)
 {
 	const struct gve_ptp *ptp = container_of(info, struct gve_ptp, info);
@@ -55,6 +61,7 @@ static const struct ptp_clock_info gve_ptp_caps = {
 	.owner          = THIS_MODULE,
 	.name		= "gve clock",
 	.gettimex64	= gve_ptp_gettimex64,
+	.settime64	= gve_ptp_settime64,
 	.do_aux_work	= gve_ptp_do_aux_work,
 };