libpayload: Add missing break statement in coreboot table parsing

Otherwise the code would try to parse GPIOs when encountering
a mainboard entry in the coreboot table. This never caused any
problems because the mainboard entry is parsed before the GPIO
entry.

Signed-off-by: Stefan Reinauer <reinauer@google.com>

Change-Id: I1443bda8585a990a39115743d48304ec4b54bccb
Reviewed-on: https://gerrit.chromium.org/gerrit/59292
Reviewed-by: Ronald G. Minnich <rminnich@chromium.org>
Commit-Queue: Stefan Reinauer <reinauer@google.com>
Tested-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/4252
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Tested-by: build bot (Jenkins)

payloads/libpayload/arch/armv7/coreboot.c

@@ -250,6 +250,7 @@ static int cb_parse_header(void *addr, int len, struct sysinfo_t *info)
 #endif
 		case CB_TAG_MAINBOARD:
 			info->mainboard = (struct cb_mainboard *)ptr;
+			break;
 #ifdef CONFIG_CHROMEOS
 		case CB_TAG_GPIO:
 			cb_parse_gpios(ptr, info);