watchdog: shwdt: Use setup_timer()

The function setup_timer combines the initialization of a timer with
the initialization of the timer's function and data fields.
The multiline code for timer initialization is now replaced
with function setup_timer.

Signed-off-by: Muhammad Falak R Wani <falakreyaz@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>