watchdog: sbc7240_wdt: Fix yet another -Wimplicit-fallthrough warning

... by moving the fall through comment outside of the code block so that
gcc sees it.

No functional changes.

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Wim Van Sebroeck <wim@linux-watchdog.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: linux-watchdog@vger.kernel.org
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20190929114649.22740-1-bp@alien8.de


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>