watchdog: rt2880_wdt: Remove assignment of dev pointer

Commit 0254e953 ("watchdog: Drop pointer to watchdog device from
struct watchdog_device") removed the dev pointer from struct
watchdog_device, but this driver was still assigning it, leading to a
compilation error:

drivers/watchdog/rt2880_wdt.c: In function ‘rt288x_wdt_probe’:
drivers/watchdog/rt2880_wdt.c:161:16: error: ‘struct watchdog_device’
has no member named ‘dev’
  rt288x_wdt_dev.dev = &pdev->dev;
                ^
scripts/Makefile.build:289: recipe for target
'drivers/watchdog/rt2880_wdt.o' failed

Fix this by removing the assignment.

Fixes: 0254e953 ("watchdog: Drop pointer to watchdog device ...")
Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
Cc: stable@vger.kernel.org # v4.5+
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>