watchdog: scx200_wdt: Use fallthrough pseudo-keyword

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1].

[1] https://www.kernel.org/doc/html/v5.7-rc7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through



Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20200717164059.GA26947@embeddedor


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