[HAMRADIO]: Fix baycom_epp.c compile failure.

Fix foobar in 15b1c0e822f578306332d4f4c449250db5c5dceb and
e8cc49bb0fdb9e18a99e6780073d1400ba2b0d1f patch series.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ax25/ax25_addr.c b/net/ax25/ax25_addr.c
index 21a0616..97a49c7 100644
--- a/net/ax25/ax25_addr.c
+++ b/net/ax25/ax25_addr.c
@@ -83,7 +83,7 @@
  */
 void asc2ax(ax25_address *addr, const char *callsign)
 {
-	char *s;
+	const char *s;
 	int n;
 
 	for (s = callsign, n = 0; n < 6; n++) {