cmd: spl: annotate switch/case fallthrough

The argument parsing in the SPL configuration command uses an implicit
switch/case fallthrough when dealing with a different number of
arguments.

Add our "fallthrough;" statement-like macro before the respective labels
in the bootm code, to avoid a warning when GCC's -Wimplicit-fallthrough
warning option is enabled.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Tom Rini <trini@konsulko.com>

cmd/spl.c

@@ -60,8 +60,10 @@ static int call_bootm(int argc, char *const argv[], const char *subcommand[])
 	switch (argc) {
 	case 3:
 		bootm_argv[4] = argv[2]; /* fdt addr */
+		fallthrough;
 	case 2:
 		bootm_argv[3] = argv[1]; /* initrd addr */
+		fallthrough;
 	case 1:
 		bootm_argv[2] = argv[0]; /* kernel addr */
 	}