cmd: missing fallthrough macro in do_pci()

Add a missing fallthrough macro to avoid a -Wimplicit-fallthrough warning.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

cmd/pci.c

@@ -517,6 +517,7 @@ static int do_pci(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
 			addr = hextoul(argv[3], NULL);
 		if (argc > 4)
 			value = hextoul(argv[4], NULL);
+		fallthrough;
 	case 'h':		/* header */
 	case 'b':		/* bars */
 		if (argc < 3)