[v2.2.x] prov/psm3: Suppress "this statement may fall through" warning

Compiler warning:

```
../prov/psm3/psm3/ptl_ips/ips_proto_connect.c: In function ‘ips_proto_build_connect_message’:
../prov/psm3/psm3/ptl_ips/ips_proto_connect.c:950:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
   if (! force)
      ^
../prov/psm3/psm3/ptl_ips/ips_proto_connect.c:953:2: note: here
  case OPCODE_DISCONNECT_REPLY:
  ^~~~
```

gcc can identify intentional fallthrough via comment, but the original
comment has an extra 'S'.

There are other approaches to address the same issue. However, none of
those are univerally supported. Here we just take the simplest fix by
removing the extra 'S' in the comment.

Signed-off-by: Jianxin Xiong <[email protected]>

Author: j-xiong

prov/psm3/psm3/ptl_ips/ips_proto_connect.c

@@ -949,7 +949,7 @@ ips_proto_build_connect_message(struct ips_proto *proto,
 	case OPCODE_DISCONNECT_REQUEST:
 		if (! force)
 			hdr->connidx |= IPS_DISCONNECT_NOFORCE;
-		/* FALLSTHROUGH */
+		/* FALLTHROUGH */
 	case OPCODE_DISCONNECT_REPLY:
 		paylen = sizeof(struct ips_connect_hdr);
 		// placeholder, typically ips_connect_hdr is sufficient