watchdog: f71808e_wdt: constify static array

The fintek_wdt_names is meant for read-only use and is currently not
modified. Mark it const to catch future writes.

Suggested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/9720c5a1efcef861da68b693453bb3eb3c21af37.1628525954.git-series.a.fatoum@pengutronix.de


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