net: phy: dp83640: use new PTP_MSGTYPE_SYNC define

Replace use of magic number with recently introduced define.

Signed-off-by: Christian Eggers <[e-mail]>
Reviewed-by: Kurt Kanzenbach <[e-mail]>
Acked-by: Richard Cochran <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/phy/dp83640.c

···
 static int is_sync(struct sk_buff *skb, int type)
 {
 	struct ptp_header *hdr;
-	u8 msgtype;
 
 	hdr = ptp_parse_header(skb, type);
 	if (!hdr)
 		return 0;
 
-	msgtype = ptp_get_msgtype(hdr, type);
-
-	return (msgtype & 0xf) == 0;
+	return ptp_get_msgtype(hdr, type) == PTP_MSGTYPE_SYNC;
 }
 
 static void dp83640_free_clocks(void)