watchdog: pcwd_usb: Avoid GFP_ATOMIC where it is not needed

There is no need to use GFP_ATOMIC here. It is a probe function, no
spinlock is taken and GFP_KERNEL is used just before and just after this
'usb_alloc_coherent()' call.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20200809071912.742836-1-christophe.jaillet@wanadoo.fr


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