xyz-modem: Add missing fallthrough annotation

Falltroughs in switch statements should be explicit.

Addresses-Coverity-ID: 131162 Missing break in switch
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/common/xyzModem.c b/common/xyzModem.c
index 09f74a1..698a538 100644
--- a/common/xyzModem.c
+++ b/common/xyzModem.c
@@ -280,6 +280,7 @@
 	    {
 	    case SOH:
 	      xyz.total_SOH++;
+	      fallthrough;
 	    case STX:
 	      if (c == STX)
 		xyz.total_STX++;